GIFT   PF    - 
the  estate  of 

Professor  William  F.  Meyer 


ASTRONOMY  UBRARJt 


SIMON    NEWCOMB 


SIDE-LIGHTS     ON 
ASTRONOMY 


AND   KINDRED   FIELDS  OF   POPULAR  SCIENCE 


ESSAYS  AND  ADDRESSES 


BY 

SIMON     NEWCOMB 


ILLUSTRATED 


NEW    YORK    AND    LONDON 
HARPER  &   BROTHERS   PUBLISHERS 


ASTRONOMY  UBRAR* 


Copyright,  1882, 1902, 1903, 1904. 1905, 1906,  by  HAKFHK  &  BROTHERS. 

Copyright,  1891,  by  LLOYD  BRYCE. 

Copyright,  1894,  by  THE  CHAUTAUQUA  PRESS. 

Copyright,  1899,  1901,  by  THE  S.  S.  McCLURE  COMPANY. 

Copyright,  1900,  by  HOUGHTON,  MIFFLIN  &  Co. 

Copyright,  1902,  by  FREDERICK  A.  RICHARDSON. 

Copyright,  1906,  by 
THE  NORTH  AMERICAN  REVIEW  PUBLISHING  Co. 


All  rights  reserved. 
Published  September,  1906. 


CONTENTS 

CHAP.  PAGE 

PREFACE vii 

I.  THE  UNSOLVED  PROBLEMS  OF  ASTRONOMY  ...  i 

II.  THE  NEW  PROBLEMS  OF  THE  UNIVERSE       ...  18 

III.  THE  STRUCTURE  OF  THE  UNIVERSE 31 

IV.  THE  EXTENT  OF  THE  UNIVERSE 60 

V.  MAKING  AND  USING  A  TELESCOPE 76 

VI.  WHAT  THE  ASTRONOMERS  ARE  DOING      ....  106 

VII.  LIFE  IN  THE  UNIVERSE •  120 

VIII.  How  THE  PLANETS  ARE  WEIGHED 133 

IX.  THE  MARINER'S  COMPASS 140 

X.  THE  FAIRYLAND  OF  GEOMETRY .  155 

XI.  THE  ORGANIZATION  OF  SCIENTIFIC  RESEARCH  .     .  165 

XII.  CAN  WE  MAKE  IT  RAIN?        182 

XIII.  THE    ASTRONOMICAL    EPHEMERIS    AND    NAUTICAL 

ALMANAC 191 

XIV.  THE  WORLD'S  DEBT  TO  ASTRONOMY 216 

XV.  AN  ASTRONOMICAL  FRIENDSHIP 227 

XVI.  THE  EVOLUTION  OF  THE  SCIENTIFIC  INVESTIGATOR  236 

XVII.  THE  EVOLUTION  OF  ASTRONOMICAL  KNOWLEDGE  .  258 

XVIII.  ASPECTS  OF  AMERICAN  ASTRONOMY 274 

XIX.  THE  UNIVERSE  AS  AN  ORGANISM 300 

XX.  THE  RELATION  OF  SCIENTIFIC  METHOD  TO  SOCIAL 

PROGRESS 312 

XXI.  THE  OUTLOOK  FOR  THE  FLYING-MACHINE     .     .     .  330 
INDEX 347 


M5770S7 


ILLUSTRATIONS 


SIMON    NEWCOMB Frontispicc* 

PHOTOGRAPH  OP  THE   CORONA  OP   THE    SUN,  TAKEN  IN 

TRIPOLI  DURING  TOTAL  ECLIPSE  OP  AUGUST  30,  1905.  Facing  p.      14 

A    TYPICAL    STAR    CLUSTER CENTAURI "              44 

THE    GLASS    DISK Page           80 

THE  OPTICIAN'S  TOOL "          81 

THE  OPTICIAN'S  TOOL "          82 

GRINDING  A  LARGE  LENS 83 

IMAGE  OF  CANDLE-FLAME  IN  OBJECT-GLASS.     ...  "         86 

TESTING  ADJUSTMENT  OF  OBJECT-GLASS "         86 

A  VERY  PRIMITIVE  MOUNTING  FOR  A  TELESCOPE  .     .  "         88 

THE  HUYGHENIAN  EYE-PIECE "         89 

SECTION  OF  THE  PRIMITIVE  MOUNTING "         90 

SPECTRAL  IMAGES  OF  STARS  J  THE  UPPER  LINE  SHOW- 
ING HOW  THEY  APPEAR  WITH  THE  EYE-PIECE  PUSH- 
ED IN;  THE  LOWER  WITH  THE  EYE-PIECE  DRAWN 

OUT Facing  p.   92 

THE  GREAT  REFRACTOR  OF  THE  NATIONAL  OBSERVA- 
TORY AT  WASHINGTON ...  "  96 

THE  "BROKEN-BACKED  COMET-SEEKER!! Page     102 

NEBULA    IN    ORION       .               Facing  p.  104 

DIP  OF  THE  MAGNETIC  NEEDLE  IN  VARIOUS   LATITUDES  Page        148 

STAR    SPECTRA Facing  p.  306 

PROFESSOR  LANGLEY'S  AIR-SHIP "       332 


PREFACE 

IN  preparing  and  issuing  this  collection  of  essays 
and  addresses,  the  author  has  yielded  to  what  he 
could  not  but  regard  as  the  too  flattering  judgment 
of  the  publishers.  Having  done  this,  it  became  in- 
cumbent to  do  what  he  could  to  justify  their  good 
opinion  by  revising  the  material  and  bringing  it  up 
to  date.  Interest  rather  than  unity  of  thought  has 
determined  the  selection. 

A  prominent  theme  in  the  collection  is  that  of  the 
structure,  extent,  and  duration  of  the  universe.  Here 
some  repetition  of  ideas  was  found  unavoidable,  in 
a  case  where  what  is  substantially  a  single  theme 
has  been  treated  in  the  various  forms  which  it  as- 
sumed in  the  light  of  constantly  growing  knowledge. 
If  the  critical  reader  finds  this  a  defect,  the  author 
can  plead  in  extenuation  only  the  difficulty  of  avoid- 
ing it  under  the  circumstances.  Although  mainly 
astronomical,  a  number  of  discussions  relating  to 
general  scientific  subjects  have  been  included. 

Acknowledgment  is  due  to  the  proprietors  of  the 
various  periodicals  from  the  pages  of  which  most  of 
the  essays  have  been  taken.  Besides  Harper's  Maga- 
zine and  the  North  American  Review,  these  include 
McClure's  Magazine,  from  which  were  taken  the  ar- 
ticles "The  Unsolved  Problems  of  Astronomy"  and 
"  How  the  Planets  are  Weighed."  "  The  Structure  of 

vii 


PREFACE 

the  Universe"  appeared  in  the  International  Monthly, 
now  the  International  Quarterly;  "  The  Outlook  for  the 
Flying-Machine"  is  mainly  from  The  New  York  In- 
dependent, but  in  part  from  McClure's  Magazine; 
"The  World's  Debt  to  Astronomy"  is  from  The 
Chautauquan;  and  "An  Astronomical  Friendship" 
from  the  Atlantic  Monthly. 

SIMON  NEWCOMB. 
WASHINGTON,  June,  1906. 


SIDE-LIGHTS  ON  ASTRONOMY 


SIDE-LIGHTS  ON  ASTRONOMY 

i 

THE  UNSOLVED  PROBLEMS  OF  ASTRONOMY 

THE  reader  already  knows  what  the  solar  system 
is:  an  immense  central  body,  the  sun,  with  a 
number  of  planets  revolving  round  it  at  various  dis- 
tances. On  one  of  these  planets  we  dwell.  Vast,  in- 
deed, are  the  distances  of  the  planets  when  measured 
by  our  terrestrial  standards.  A  cannon  -  ball  fired 
from  the  earth  to  celebrate  the  signing  of  the  Dec- 
laration of  Independence,  and  continuing  its  course 
ever  since  with  a  velocity  of  eighteen  hundred  feet 
per  second,  would  not  yet  be  half-way  to  the  orbit  of 
Neptune,  the  outer  planet.  And  yet  the  thousands 
of  stars  which  stud  the  heavens  are  at  distances  so 
much  greater  than  that  of  Neptune  that  our  solar 
system  is  like  a  little  colony,  separated  from  the  rest 
of  the  universe  by  an  ocean  of  void  space  almost  im- 
measurable in  extent.  The  orbit  of  the  earth  round 
the  sun  is  of  such  size  that  a  railway  train  running 
sixty  miles  an  hour,  with  never  a  stop,  would  take 
about  three  hundred  and  fifty  years  to  cross  it. 
Represent  this  orbit  by  a  lady's  finger -ring.  Then 
the  nearest  fixed  star  will  be  about  a  mile  and  a  half 


SIDE-LIGHTS    ON    ASTRONOMY 

away ;  the  next  more  than  two  miles ;  a  few  more  from 
three  to  twenty  miles;  the  great  body  at  scores  or 
hundreds  of  miles.  Imagine  the  stars  thus  scattered 
from  the  Atlantic  to  the  Mississippi,  and  keep  this 
little  finger -ring  in  mind  as  the  orbit  of  the  earth, 
and  one  may  have  some  idea  of  the  extent  of  the 
universe. 

One  of  the  most  beautiful  stars  in  the  heavens,  and 
one  that  can  be  seen  most  of  the  year,  is  a  Lyres,  or 
Alpha  of  the  Lyre,  known  also  as  Vega.  In  a  spring 
evening  it  may  be  seen  in  the  northeast,  in  the  later 
summer  near  the  zenith,  in  the  autumn  in  the  north- 
west. On  the  scale  we  have  laid  down  with  the 
earth's  orbit  as  a  finger-ring,  its  distance  would  be 
some  eight  or  ten  miles.  The  small  stars  around  it 
in  the  same  constellation  are  probably  ten,  twenty, 
or  fifty  times  as  far. 

Now,  the  greatest  fact  which  modern  science  has 
brought  to  light  is  that  our  whole  solar  system,  in- 
cluding the  sun,  with  all  its  planets,  is  on  a  journey 
towards  the  constellation  Lyra.  During  our  whole 
lives,  in  all  probability  during  the  whole  of  human 
history,  we  have  been  flying  unceasingly  towards 
this  beautiful  constellation  with  a  speed  to  which  no 
motion  on  earth  can  compare.  The  speed  has  recent- 
ly been  determined  with  a  fair  degree  of  certainty, 
though  not  with  entire  exactness;  it  is  about  ten 
miles  a  second,  and  therefore  not  far  from  three  hun- 
dred millions  of  miles  a  year.  But  whatever  it  may 
be,  it  is  unceasing  and  unchanging;  for  us  mortals 
eternal.  We  are  nearer  the  constellation  by  five  or 
six  hundred  miles  every  minute  we  live;  we  are  nearer 
to  it  now  than  we  were  ten  years  ago  by  thousands 
of  millions  of  miles,  and  every  future  generation  of 


UNSOLVED    PROBLEMS 

our  race  will  be  nearer  than  its  predecessor  by  thou- 
sands of  millions  of  miles. 

When,  where,  and  how,  if  ever,  did  this  journey 
begin — when,  where,  and  how,  if  ever,  will  it  end? 
This  is  the  greatest  of  the  unsolved  problems  of  as- 
tronomy. An  astronomer  who  should  watch  the 
heavens  for  ten  thousand  years  might  gather  some 
faint  suggestion  of  an  answer,  or  he  might  not.  All 
we  can  do  is  to  seek  for  some  hints  by  study  and 
comparison  with  other  stars. 

The  stars  are  suns.  To  put  it  in  another  way,  the 
sun  is  one  of  the  stars,  and  rather  a  small  one  at  that. 
If  the  sun  is  moving  in  the  way  I  have  described,  may 
not  the  stars  also  be  in  motion,  each  on  a  journey  of 
its  own  through  the  wilderness  of  space?  To  this 
question  astronomy  gives  an  affirmative  answer. 
Most  of  the  stars  nearest  to  us  are  found  to  be  in 
motion,  some  faster  than  the  sun,  some  more  slowly, 
and  the  same  is  doubtless  true  of  all ;  only  the  century 
of  accurate  observations  at  our  disposal  does  not 
show  the  motion  of  the  distant  ones.  A  given  mo- 
tion seems  slower  the  more  distant  the  moving  body; 
we  have  to  watch  a  steamship  on  the  horizon  some 
little  time  to  see  that  she  moves  at  all.  Thus  it  is 
that  the  unsolved  problem  of  the  motion  of  our  sun 
is  only  one  branch  of  a  yet  more  stupendous  one: 
What  mean  the  motions  of  the  stars — how  did  they 
begin,  and  how,  if  ever,  will  they  end  ?  So  far  as  we 
can  yet  see,  each  star  is  going  straight  ahead  on  its 
own  journey,  without  regard  to  its  neighbors,  if  other 
stars  can  be  so  called.  Is  each  describing  some  vast 
orbit  which,  though  looking  like  a  straight  line  dur- 
ing the  short  period  of  our  observation,  will  really 
be  seen  to  curve  after  ten  thousand  or  a  hundred 

3 


SIDE-LIGHTS    ON    ASTRONOMY 

thousand  years,  or  will  it  go  straight  on  forever?  If 
the  laws  of  motion  are  true  for  all  space  and  all  time, 
as  we  are  forced  to  believe,  then  each  moving  star 
will  go  on  in  an  unbending  line  forever  unless  hindered 
by  the  attraction  of  other  stars.  If  they  go  on  thus, 
they  must,  after  countless  years,  scatter  in  all  direc- 
tions, so  that  the  inhabitants  of  each  shall  see  only 
a  black,  starless  sky. 

Mathematical  science  can  throw  only  a  few  glim- 
mers of  light  on  the  questions  thus  suggested.  From 
what  little  we  know  of  the  masses,  distances,  and 
numbers  of  the  stars  we  see  a  possibility  that  the 
more  slow-moving  ones  may,  in  long  ages,  be  stopped 
in  their  onward  courses  or  brought  into  orbits  of 
some  sort  by  the  attraction  of  their  millions  of  fellows. 
But  it  is  hard  to  admit  even  this  possibility  in  the 
case  of  the  swift-moving  ones.  Attraction,  varying 
as  the  inverse  square  of  the  distance,  diminishes  so 
rapidly  as  the  distance  increases  that,  at  the  dis- 
tances which  separate  the  stars,  it  is  small  indeed. 
We  could  not,  with  the  most  delicate  balance  that 
science  has  yet  invented,  even  show  the  attraction 
of  the  greatest  known  star.  So  far  as  we  know,  the 
two  swiftest-moving  stars  are,  first,  Arcturus,  and, 
second,  one  known  in  astronomy  as  1830  Groom- 
bridge,  the  latter  so  called  because  it  was  first 
observed  by  the  astronomer  Groombridge,  and  is 
numbered  1830  in  his  catalogue  of  stars.  If  our 
determinations  of  the  distances  of  these  bodies  are 
to  be  relied  on,  the  velocity  of  their  motion  can- 
not be  much  less  than  two  hundred  miles  a  second. 
They  would  make  the  circuit  of  the  earth  every  two 
or  three  minutes.  A  body  massive  enough  to  con- 
trol this  motion  would  throw  a  large  part  of  the 

4 


UNSOLVED    PROBLEMS 

universe  into  disorder.  Thus  the  problem  where 
these  stars  came  from  and  where  they  are  going  is 
for  us  insoluble,  and  is  all  the  more  so  from  the  fact 
that  the  swiftly  moving  stars  are  moving  in  different 
directions  and  seem  to  have  no  connection  with  each 
other  or  with  any  known  star. 

It  must  not  be  supposed  that  these  enormous 
velocities  seem  so  to  us.  Not  one  of  them,  even  the 
greatest,  would  be  visible  to  the  naked  eye  until 
after  years  of  watching.  On  our  finger-ring  scale, 
1830  Groombridge  would  be  some  ten  miles  and  Arc- 
turus  thirty  or  forty  miles  away.  Either  of  them 
would  be  moving  only  two  or  three  feet  in  a  year. 
To  the  oldest  Assyrian  priests  Lyra  looked  much  as 
it  does  to  us  to-day.  Among  the  bright  and  well- 
known  stars  Arcturus  has  the  most  rapid  apparent 
motion,  yet  Job  himself  would  not  to-day  see  that 
its  position  had  changed,  unless  he  had  noted  it 
with  more  exactness  than  any  astronomer  of  his 
time. 

Another  unsolved  problem  among  the  greatest 
which  present  themselves  to  the  astronomer  is  that 
of  the  size  of  the  universe  of  stars.  We  know  that 
several  thousand  of  these  bodies  are  visible  to  the 
naked  eye;  moderate  telescopes  show  us  millions; 
our  giant  telescopes  of  the  present  time,  when  used 
as  cameras  to  photograph  the  heavens,  show  a  num- 
ber past  count,  perhaps  one  hundred  millions.  Are  all 
these  stars  only  those  few  which  happen  to  be  near 
us  in  a  universe  extending  out  without  end,  or  do 
they  form  a  collection  of  stars  outside  of  which  is 
empty  infinite  space?  In  other  words,  has  the  uni- 
verse a  boundary?  Taken  in  its  widest  scope  this 
question  must  always  remain  unanswered  by  us  mor- 

5 


SIDE-LIGHTS    ON    ASTRONOMY 

tals  because,  even  if  we  should  discover  a  boundary 
within  which  all  the  stars  and  clusters  we  ever  can 
know  are  contained,  and  outside  of  which  is  empty 
space,  still  we  could  never  prove  that  this  space  is 
empty  out  to  an  infinite  distance.  Far  outside  of 
what  we  call  the  universe  might  still  exist  other  uni- 
verses which  we  can  never  see. 

It  is  a  great  encouragement  to  the  astronomer  that, 
although  he  cannot  yet  set  any  exact  boundary  to 
this  universe  of  ours,  he  is  gathering  faint  indications 
that  it  has  a  boundary,  which  his  successors  not  many 
generations  hence  may  locate  so  that  the  astronomer 
shall  include  creation  itself  within  his  mental  grasp. 
It  can  be  shown  mathematically  that  an  infinitely 
extended  system  of  stars  would  fill  the  heavens  with 
a  blaze  of  light  like  that  of  the  noonday  sun.  As  no 
such  effect  is  produced,  it  may  be  concluded  that  the 
universe  has  a  boundary.  But  this  does  not  enable 
us  to  locate  the  boundary,  nor  to  say  how  many  stars 
may  lie  outside  the  farthest  stretches  of  telescopic 
vision.  Yet  by  patient  research  we  are  slowly  throw- 
ing light  on  these  points  and  reaching  inferences 
which,  not  many  years  ago,  would  have  seemed  for- 
ever beyond  our  powers. 

Every  one  now  knows  that  the  Milky  Way,  that 
girdle  of  light  which  spans  the  evening  sky,  is  formed 
of  clouds  of  stars  too  minute  to  be  seen  by  the  unaided 
vision.  It  seems  to  form  the  base  on  which  the  uni- 
verse is  built  and  to  bind  all  the  stars  into  a  system. 
It  comprises  by  far  the  larger  number  of  stars  that 
the  telescope  has  shown  to  exist.  Those  we  see  with 
the  naked  eye  are  almost  equally  scattered  over  the 
sky.  But  the  number  which  the  telescope  shows  us 
become  more  and  more  condensed  in  the  Milky  Way 

6 


UNSOLVED    PROBLEMS 

as  telescope  power  is  increased.  The  number  of  new 
stars  brought  out  with  our  greatest  power  is  vastly 
greater  in  the  Milky  Way  than  in  the  rest  of  the  sky, 
so  that  the  former  contains  a  great  majority  of  the 
stars.  What  is  yet  more  curious,  spectroscopic  re- 
search has  shown  that  a  particular  kind  of  stars, 
those  formed  of  heated  gas,  are  yet  more  condensed 
in  the  central  circle  of  this  band ;  if  they  were  visible 
to  the  naked  eye,  we  should  see  them  encircling  the 
heavens  as  a  narrow  girdle  forming  perhaps  the  base 
of  our  whole  system  of  stars.  This  arrangement  of 
the  gaseous  or  vaporous  stars  is  one  of  the  most  singu- 
lar facts  that  modern  research  has  brought  to  light. 
It  seems  to  show  that  these  particular  stars  form  a 
system  of  their  own ;  but  how  such  a  thing  can  be  we 
are  still  unable  to  see. 

The  question  of  the  form  and  extent  of  the  Milky 
Way  thus  becomes  the  central  one  of  stellar  astron- 
omy. Sir  William  Herschel  began  by  trying  to  sound 
its  depths ;  at  one  time  he  thought  he  had  succeeded ; 
but  before  he  died  he  saw  that  they  were  unfathom- 
able with  his  most  powerful  telescopes.  Even  to- 
day he  would  be  a  bold  astronomer  who  would  pro- 
fess to  say  with  certainty  whether  the  smallest  stars 
we  can  photograph  are  at  the  boundary  of  the  system. 
Before  we  decide  this  point  we  must  have  some  idea 
of  the  form  and  distance  of  the  cloudlike  masses  of 
stars  which  form  our  great  celestial  girdle.  A  most 
curious  fact  is  that  our  solar  system  seems  to  be  in 
the  centre  of  this  galactic  universe,  because  the  Milky 
Way  divides  the  heavens  into  two  equal  parts,  and 
seems  equally  broad  at  all  points.  Were  we  looking 
at  such  a  girdle  as  this  from  one  side  or  the  other, 
this  appearance  would  not  be  presented.  But  let  us 

7 


SIDE-LIGHTS    ON    ASTRONOMY 

not  be  too  bold.  Perhaps  we  are  the  victims  of  some 
fallacy,  as  Ptolemy  was  when  he  proved,  by  what 
looked  like  sound  reasoning,  based  on  undeniable 
facts,  that  this  earth  of  ours  stood  at  rest  in  the 
centre  of  the  heavens! 

A  related  problem,  and  one  which  may  be  of  su- 
preme importance  to  the  future  of  our  race,  is,  What 
is  the  source  of  the  heat  radiated  by  the  sun  and  stars  ? 
We  know  that  life  on  the  earth  is  dependent  on  the 
heat  which  the  sun  sends  it.  If  we  were  deprived  of 
this  heat  we  should  in  a  few  days  be  enveloped  in  a 
frost  which  would  destroy  nearly  all  vegetation,  and  in 
a  few  months  neither  man  nor  animal  would  be  alive, 
unless  crouching  over  fires  soon  to  expire  for  want  of 
fuel.  We  also  know  that,  at  a  time  which  is  geo- 
logically recent,  the  whole  of  New  England  was  cov- 
ered with  a  sheet  of  ice,  hundreds  or  even  thousands 
of  feet  thick,  above  which  no  mountain  but  Washing- 
ton raised  its  head.  It  is  quite  possible  that  a  small 
diminution  in  the  supply  of  heat  sent  us  by  the  sun 
would  gradually  reproduce  the  great  glacier,  and  once 
more  make  the  Eastern  States  like  the  pole.  But  the 
fact  is  that  observations  of  temperature  in  various 
countries  for  the  last  two  or  three  hundred  years  do 
not  show  any  change  in  climate  which  can  be  attrib- 
uted to  a  variation  in  the  amount  of  heat  received 
from  the  sun. 

The  acceptance  of  this  theory  of  the  heat  of  those 
heavenly  bodies  which  shine  by  their  own  light — sun, 
stars,  and  nebulas — still  leaves  open  a  problem  that 
looks  insoluble  with  our  present  knowledge.  What 
becomes  of  the  great  flood  of  heat  and  light  which  the 
sun  and  stars  radiate  into  empty  space  with  a  velocity 
of  one  hundred  and  eighty  thousand  miles  a  second? 

8 


UNSOLVED    PROBLEMS 

Only  a  very  small  fraction  of  it  can  be  received  by 
the  planets  or  by  other  stars,  because  these  are  mere 
points  compared  with  their  distance  from  us.  Tak- 
ing the  teaching  of  our  science  just  as  it  stands,  we 
should  say  that  all  this  heat  continues  to  move  on 
through  infinite  space  forever.  In  a  few  thousand 
years  it  reaches  the  probable  confines  of  our  great 
universe.  But  we  know  of  no  reason  why  it  should 
stop  here.  During  the  hundreds  of  millions  of  years 
since  all  our  stars  began  to  shine,  has  the  first  ray 
of  light  and  heat  kept  on  through  space  at  the  rate  of 
one  hundred  and  eighty  thousand  miles  a  second,  and 
will  it  continue  to  go  on  for  ages  to  come?  If  so, 
think  of  its  distance  now,  and  think  of  its  still 
going  on,  to  be  forever  wasted!  Rather  say  that 
the  problem,  What  becomes  of  it?  is  as  yet  un- 
solved. 

Thus  far  I  have  described  the  greatest  of  problems ; 
those  which  we  may  suppose  to  concern  the  inhabi- 
tants of  millions  of  worlds  revolving  round  the  stars 
as  much  as  they  concern  us.  Let  us  now  come  down 
from  the  starry  heights  to  this  little  colony  where  we 
live,  the  solar  system.  Here  we  have  the  great  ad- 
vantage of  being  better  able  to  see  what  is  going  on, 
owing  to  the  comparative  nearness  of  the  planets. 
When  we  learn  that  these  bodies  are  like  our  earth 
in  form,  size,  and  motions,  the  first  question  we  ask 
is,  Could  we  fly  from  planet  to  planet  and  light  on  the 
surface  of  each,  what  sort  of  scenery  would  meet  our 
eyes?  Mountain,  forest,  and  field,  a  dreary  waste, 
or  a  seething  caldron  larger  than  our  earth  ?  If  solid 
land  there  is,  would  we  find  on  it  the  homes  of  in- 
telligent beings,  the  lairs  of  wild  beasts,  or  no  living 
thing  at  all?  Could  we  breathe  the  air,  would  we 

9 


SIDE-LIGHTS    ON    ASTRONOMY 

choke  for  breath  or  be  poisoned  by  the  fumes  of  some 
noxious  gas? 

To  most  of  these  questions  science  cannot  as  yet 
give  a  positive  answer,  except  in  the  case  of  the  moon. 
Our  satellite  is  so  near  us  that  we  can  see  it  has  no 
atmosphere  and  no  water,  and  therefore  cannot  be 
the  abode  of  life  like  ours.  The  contrast  of  its  eternal 
deadness  with  the  active  life  around  us  is  great  indeed. 
Here  we  have  weather  of  so  many  kinds  that  we  never 
tire  of  talking  about  it.  But  on  the  moon  there  is  no 
weather  at  all.  On  our  globe  so  many  things  are  con- 
stantly happening  that  our  thousands  of  daily  jour- 
nals cannot  begin  to  record  them.  But  on  the  dreary, 
rocky  wastes  of  the  moon  nothing  ever  happens.  So 
far  as  we  can  determine,  every  stone  that  lies  loose 
on  its  surface  has  lain  there  through  untold  ages,  un- 
changed and  unmoved. 

We  cannot  speak  so  confidently  of  the  planets. 
The  most  powerful  telescopes  yet  made,  the  most 
powerful  we  can  ever  hope  to  make,  would  scarcely 
shows  us  mountains,  or  lakes,  rivers,  or  fields  at  a 
distance  of  fifty  millions  of  miles.  Much  less  would 
they  show  us  any  works  of  man.  Pointed  at  the  two 
nearest  planets,  Venus  and  Mars,  they  whet  our  cu- 
riosity more  than  they  gratify  it.  Especially  is  this 
the  case  with  Venus.  Ever  since  the  telescope  was 
invented  observers  have  tried  to  find  the  time  of  rota- 
tion of  this  planet  on  its  axis.  Some  have  reached 
one  conclusion,  some  another,  while  the  wisest  have 
only  doubted.  The  great  Herschel  claimed  that  the 
planet  was  so  enveloped  in  vapor  or  clouds  that  no 
permanent  features  could  be  seen  on  its  surface. 
The  best  equipped  recent  observers  think  they  see 
faint,  shadowy  patches,  which  remain  the  same  from 

10 


UNSOLVED    PROBLEMS 

day  to  day,  and  which  show  that  the  planet  always 
presents  the  same  face  to  the  sun,  as  the  moon  does 
to  the  earth.  Others  do  not  accept  this  conclusion  as 
proved,  believing  that  these  patches  may  be  nothing 
more  than  variations  of  light,  shade,  and  color  caused 
by  the  reflection  of  the  sun's  light  at  various  angles 
from  different  parts  of  the  planet. 

There  is  also  some  mystery  about  the  atmosphere 
of  this  planet.  When  Venus  passes  nearly  between 
us  and  the  sun,  her  dark  hemisphere  is  turned  tow- 
ards us,  her  bright  one  being  always  towards  the  sun. 
But  she  is  not  exactly  on  a  line  with  the  sun  except 
on  the  very  rare  occasions  of  a  transit  across  the 
sun's  disk.  Hence,  on  ordinary  occasions,  when  she 
seems  very  near  on  a  line  with  the  sun,  we  see  a  very 
small  part  of  the  illuminated  hemisphere,  which  now 
presents  the  form  of  a  very  thin  crescent  like  the 
new  moon.  And  this  crescent  is  supposed  to  be  a 
little  broader  than  it  would  be  if  only  half  the  planet 
were  illuminated,  and  to  encircle  rather  more  than 
half  the  planet.  Now,  this  is  just  the  effect  that 
would  be  produced  by  an  atmosphere  refracting  the 
sun's  light  around  the  edge  of  the  illuminated  hemi- 
sphere. 

The  difficulty  of  observations  of  this  kind  is  such 
that  the  conclusion  may  be  open  to  doubt.  What  is 
seen  during  transits  of  Venus  over  the  sun's  disk  leads 
to  more  certain,  but  yet  very  puzzling,  conclusions. 
The  writer  will  describe  what  he  saw  at  the  Cape  of 
Good  Hope  during  the  transit  of  December  5,  1882. 
As  the  dark  planet  impinged  on  the  bright  sun,  it  of 
course  cut  out  a  round  notch  from  the  edge  of  the 
sun.  At  first,  when  this  notch  was  small,  nothing 
could  be  seen  of  the  outline  of  that  part  of  the  planet 

ii 


SIDE-LIGHTS    ON    ASTRONOMY 

which  was  outside  the  sun.  But  when  half  the  planet 
was  on  the  sun,  the  outline  of  the  part  still  off  the 
sun  was  marked  by  a  slender  arc  of  light.  A  curious 
fact  was  that  this  arc  did  not  at  first  span  the  whole 
outline  of  the  planet,  but  only  showed  at  one  or  two 
points.  In  a  few  moments  another  part  of  the  out- 
line appeared,  and  then  another,  until,  at  last,  the  arc 
of  light  extended  around  the  complete  outline.  All 
this  seems  to  show  that  while  the  planet  has  an  at- 
mosphere, it  is  not  transparent  like  ours,  but  is  so 
filled  with  mist  and  clouds  that  the  sun  is  seen 
through  it  only  as  if  shining  in  a  fog. 

Not  many  years  ago  the  planet  Mars,  which  is  the 
next  one  outside  of  us,  was  supposed  to  have  a  sur- 
face like  that  of  our  earth.  Some  parts  were  of  a 
dark  greenish  gray  hue;  these  were  supposed  to  be 
seas  and  oceans.  Other  parts  had  a  bright,  warm 
tint ;  these  were  supposed  to  be  the  continents.  Dur- 
ing the  last  twenty  years  much  has  been  learned  as 
to  how  this  planet  looks,  and  the  details  of  its  sur- 
face have  been  mapped  by  several  observers,  using 
the  best  telescopes  under  the  most  favorable  condi- 
tions of  air  and  climate.  And  yet  it  must  be  con- 
fessed that  the  result  of  this  labor  is  not  altogether 
satisfactory.  It  seems  certain  that  the  so-called  seas 
are  really  land  and  not  water.  When  it  comes  to 
comparing  Mars  with  the  earth,  we  cannot  be  cer- 
tain of  more  than  a  single  point  of  resemblance.  This 
is  that  during  the  Martian  winter  a  white  cap,  as  of 
snow,  is  formed  over  the  pole,  which  partially  melts 
away  during  the  summer.  The  conclusion  that  there 
are  oceans  whose  evaporation  forms  clouds  which  give 
rise  to  this  snow  seems  plausible.  But  the  telescope 
shows  no  clouds,  and  nothing  to  make  it  certain  that 

12 


UNSOLVED    PROBLEMS 

there  is  an  atmosphere  to  sustain  them.  There  is 
no  certainty  that  the  white  deposit  is  what  we  call 
snow ;  perhaps  it  is  not  formed  of  water  at  all.  The 
most  careful  studies  of  the  surface  of  this  planet,  un- 
der the  best  conditions,  are  those  made  at  the  Lowell 
Observatory  at  Flagstaff,  Arizona.  Especially  won- 
derful is  the  system  of  so-called  canals,  first  seen  by 
Schiaparelli,  but  mapped  in  great  detail  at  Flagstaff. 
But  the  nature  and  meaning  of  these  mysterious  lines 
are  still  to  be  discovered.  The  result  is  that  the  ques- 
tion of  the  real  nature  of  the  surface  of  Mars  and  of 
what  we  should  see  around  us  could  we  land  upon  it 
and  travel  over  it  are  still  among  the  unsolved  prob- 
lems of  astronomy. 

If  this  is  the  case  with  the  nearest  planets  that  we 
can  study,  how  is  it  with  more  distant  ones  ?  Jupiter 
is  the  only  one  of  these  of  the  condition  of  whose  sur- 
face we  can  claim  to  have  definite  knowledge.  But 
even  this  knowledge  is  meagre.  The  substance  of 
what  we  know  is  that  its  surface  is  surrounded  by 
layers  of  what  look  like  dense  clouds,  through  which 
nothing  can  certainly  be  seen. 

I  have  already  spoken  of  the  heat  of  the  sun  and 
its  probable  origin.  But  the  question  of  its  heat, 
though  the  most  important,  is  not  the  only  one  that 
the  sun  offers  us.  What  is  the  sun?  When  we  say 
that  it  is  a  very  hot  globe,  more  than  a  million  times 
as  large  as  the  earth,  and  hotter  than  any  furnace 
that  man  can  make,  so  that  literally  "the  elements 
melt  with  fervent  heat"  even  at  its  surface,  while  in- 
side they  are  all  vaporized,  we  have  told  the  most 
that  we  know  as  to  what  the  sun  really  is.  Of  course 
we  know  a  great  deal  about  the  spots,  the  rotation 
of  the  sun  on  its  axis,  the  materials  of  which  it  is 

13 


SIDE-LIGHTS    ON    ASTRONOMY 

composed,  and  how  its  surroundings  look  during  a 
total  eclipse.  But  all  this  does  not  answer  our  ques- 
tion. There  are  several  mysteries  which  ingenious 
men  have  tried  to  explain,  but  they  cannot  prove 
their  explanations  to  be  correct.  One  is  the  cause 
and  nature  of  the  spots.  Another  is  that  the  shin- 
ing surface  of  the  sun,  the  "photosphere,"  as  it  is 
technically  called,  seems  so  calm  and  quiet  while 
forces  are  acting  within  it  of  a  magnitude  quite  be- 
yond our  conception.  Flames  in  which  our  earth 
and  everything  on  it  would  be  engulfed  like  a  boy's 
marble  in  a  blacksmith's  forge  are  continually  shoot- 
ing up  to  a  height  of  tens  of  thousands  of  miles.  One 
would  suppose  that  internal  forces  capable  of  doing 
this  would  break  the  surface  up  into  billows  of  fire 
a  thousand  miles  high ;  but  we  see  nothing  of  the  kind. 
The  surface  of  the  sun  seems  almost  as  placid  as  a 
lake. 

Yet  another  mystery  is  the  corona  of  the  sun.  This 
is  something  we  should  never  have  known  to  exist 
if  the  sun  were  not  sometimes  totally  eclipsed  by  the 
dark  body  of  the  moon.  On  these  rare  occasions  the 
sun  is  seen  to  be  surrounded  by  a  halo  of  soft,  white 
light,  sending  out  rays  in  various  directions  to  great 
distances.  This  halo  is  called  the  corona,  and  has 
been  most  industriously  studied  and  photographed 
during  nearly  every  total  eclipse  for  thirty  years. 
Thus  we  have  learned  much  about  how  it  looks  and 
what  its  shape  is.  It  has  a  fibrous,  woolly  structure, 
a  little  like  the  loose  end  of  a  much -worn  hempen 
rope.  A  certain  resemblance  has  been  seen  between 
the  form  of  these  seeming  fibres  and  that  of  the  lines 
in  which  iron  filings  arrange  themselves  when  sprin- 
kled on  paper  over  a  magnet.  It  has  hence  been  in- 

14 


PHOTOGRAPH    OF    THE     CORONA    OF    THE    SUN,    TAKEN    IN 
TRIPOLI    DURING   TOTAL    ECLIPSE    OF    AUGUST    30,    1905 


UNSOLVED    PROBLEMS 

f erred  that  the  sun  has  magnetic  properties,  a  con- 
clusion which,  in  a  general  way,  is  supported  by  many 
other  facts.  Yet  the  corona  itself  remains  no  less  an 
unexplained  phenomenon. 

A  phenomenon  almost  as  mysterious  as  the  solar 
corona  is  the  "zodiacal  light,"  which  any  one  can  see 
rising  from  the  western  horizon  just  after  the  end 
of  twilight  on  a  clear  winter  or  spring  evening.  The 
most  plausible  explanation  is  that  it  is  due  to  a  cloud 
of  small  meteoric  bodies  revolving  round  the  sun. 
We  should  hardly  doubt  this  explanation  were  it  not 
that  this  light  has  a  yet  more  mysterious  append- 
age, commonly  called  the  Gegenschein,  or  counter- 
glow.  This  is  a  patch  of  light  in  the  sky  in  a  di- 
rection exactly  opposite  that  of  the  sun.  It  is  so 
faint  that  it  can  be  seen  only  by  a  practised  eye 
under  the  most  favorable  conditions.  But  it  is  al- 
ways there.  The  latest  suggestion  is  that  it  is  a 
tail  of  the  earth,  of  the  same  kind  as  the  tail  of  a 
comet ! 

We  know  that  the  motions  of  the  heavenly  bodies 
are  predicted  with  extraordinary  exactness  by  the 
theory  of  gravitation.  When  one  finds  that  the 
exact  path  of  the  moon's  shadow  on  the  earth  during 
a  total  eclipse  of  the  sun  can  be  mapped  out  many 
years  in  advance,  and  that  the  planets  follow  the  pre- 
dictions of  the  astronomer  so  closely  that,  if  you 
could  see  the  predicted  planet  as  a  separate  object,  it 
would  look,  even  in  a  good  telescope,  as  if  it  exactly 
fitted  over  the  real  planet,  one  thinks  that  here  at 
least  is  a  branch  of  astronomy  which  is  simply  per- 
fect. And  yet  the  worlds  themselves  show  slight 
deviations  in  their  movements  which  the  astronomer 
cannot  always  explain,  and  which  may  be  due  to 

15 


SIDE-LIGHTS    ON    ASTRONOMY 

some  hidden  cause  that,  when  brought  to  light,  shall 
lead  to  conclusions  of  the  greatest  importance  to  our 
race. 

One  of  these  deviations  is  in  the  rotation  of  the 
earth.  Sometimes,  for  several  years  at  a  time,  it 
seems  to  revolve  a  little  faster,  and  then  again  a  little 
slower.  The  changes  are  very  slight;  they  can  be 
detected  only  by  the  most  laborious  and  refined 
methods;  yet  they  must  have  a  cause,  and  we  should 
like  to  know  what  that  cause  is. 

The  moon  shows  a  similar  irregularity  of  motion. 
For  half  a  century,  perhaps  through  a  whole  century, 
she  will  go  around  the  earth  a  little  ahead  of  her  regu- 
lar rate,  and  then  for  another  half -century  or  more 
she  will  fall  behind.  The  changes  are  very  small; 
they  would  never  have  been  seen  with  the  unaided  eye, 
yet  they  exist.  What  is  their  cause?  Mathemati- 
cians have  vainly  spent  years  of  study  in  trying  to 
answer  this  question. 

The  orbit  of  Mercury  is  found  by  observations  to 
have  a  slight  motion  which  mathematicians  have 
vainly  tried  to  explain.  For  some  time  it  was  sup- 
posed to  be  caused  by  the  attraction  of  an  unknown 
planet  between  Mercury  and  the  sun,  and  some  were 
so  sure  of  the  existence  of  this  planet  that  they  gave 
it  a  name,  calling  it  Vulcan.  But  of  late  years  it  has 
become  reasonably  certain  that  no  planet  large  enough 
to  produce  the  effect  observed  can  be  there.  So  thor- 
oughly has  every  possible  explanation  been  sifted 
out  and  found  wanting,  that  some  astronomers  are 
now  inquiring  whether  the  law  of  gravitation  itself 
may  not  be  a  little  different  from  what  has  always 
been  supposed .  A  very  slight  deviation ,  indeed ,  would 
account  for  the  facts,  but  cautious  astronomers  want 

16 


UNSOLVED    PROBLEMS 

other  proofs  before  regarding  the  deviation  of  gravi- 
tation as  an  established  fact. 

Intelligent  men  have  sometimes  inquired  how,  after 
devoting  so  much  work  to  the  study  of  the  heavens, 
anything  can  remain  for  astronomers  to  find  out.  It 
is  a  curious  fact  that,  although  they  were  never 
learning  so  fast  as  at  the  present  day,  yet  there 
seems  to  be  more  to  learn  now  than  there  ever  was 
before.  Great  and  numerous  as  are  the  unsolved 
problems  of  our  science,  knowledge  is  now  advancing 
into  regions  which,  a  few  years  ago,  seemed  inacces- 
sible. Where  it  will  stop  none  can  say. 


II 

THE   NEW   PROBLEMS  OF  THE   UNIVERSE 

HPHE  achievements  of  the  nineteenth  century  are 
1  still  a  theme  of  congratulation  on  the  part  of 
all  who  compare  the  present  state  of  the  world  with 
that  of  one  hundred  years  ago.  And  yet,  if  we  should 
fancy  the  most  sagacious  prophet,  endowed  with  a 
brilliant  imagination,  to  have  set  forth  in  the  year 
1806  the  problems  that  the  century  might  solve  and 
the  things  which  it  might  do,  we  should  be  surprised 
to  see  how  few  of  his  predictions  had  come  to  pass. 
He  might  have  fancied  aerial  navigation  and  a  num- 
ber of  other  triumphs  of  the  same  class,  but  he  would 
hardly  have  had  either  steam  navigation  or  the  tele- 
graph in  his  picture.  In  1856  an  article  appeared  in 
Harper's  Magazine  depicting  some  anticipated  feat- 
ures of  life  in  A.D.  3000.  We  have  since  made  great 
advances,  but  they  bear  little  resemblance  to  what 
the  writer  imagined.  He  did  not  dream  of  the  tele- 
phone, but  did  describe  much  that  has  not  yet  come 
to  pass  and  probably  never  will. 

The  fact  is  that,  much  as  the  nineteenth  century 
has  done,  its  last  work  was  to  amuse  itself  by  setting 
forth  more  problems  for  this  century  to  solve  than 
it  has  ever  itself  succeeded  in  mastering.  We  should 
not  be  far  wrong  in  saying  that  to-day  there  are  more 
riddles  in  the  universe  than  there  were  before  men 

18 


NEW  PROBLEMS  OF  THE  UNIVERSE 

knew  that  it  contained  anything  more  than  the  ob- 
jects they  could  see. 

So  far  as  mere  material  progress  is  concerned,  it 
may  be  doubtful  whether  anything  so  epoch-making 
as  the  steam-engine  or  the  telegraph  is  held  in  store 
for  us  by  the  future.  But  in  the  field  of  purely 
scientific  discovery  we  are  finding  a  crowd  of  things 
of  which  our  philosophy  did  not  dream  even  ten 
years  ago. 

The  greatest  riddles  which  the  nineteenth  century 
has  bequeathed  to  us  relate  to  subjects  so  widely 
separated  as  the  structure  of  the  universe  and  the 
structure  of  atoms  of  matter.  We  see  more  and  more 
of  these  structures,  and  we  see  more  and  more  of 
unity  everywhere,  and  yet  new  facts  difficult  of  ex- 
planation are  being  added  more  rapidly  than  old 
facts  are  being  explained. 

We  all  know  that  the  nineteenth  century  was 
marked  by  a  separation  of  the  sciences  into  a  vast 
number  of  specialties,  to  the  subdivisions  of  which 
one  could  see  no  end.  But  the  great  work  of  the 
twentieth  century  will  be  to  combine  many  of  these 
specialties.  The  physical  philosopher  of  the  present 
time  is  directing  his  thought  to  the  demonstration  of 
the  unity  of  creation.  Astronomical  and  physical 
researches  are  now  being  united  in  a  way  which  is 
bringing  the  infinitely  great  and  the  infinitely  small 
into  one  field  of  knowledge.  Ten  years  ago  the  atoms 
of  matter,  of  which  it  takes  millions  of  millions  to 
make  a  drop  of  water,  were  the  minutest  objects  with 
which  science  could  imagine  itself  to  be  concerned. 
Now  a  body  of  experimentalists,  prominent  among 
whom  stand  Professors  J.  J.  Thompson,  Becquerel, 
and  Roentgen,  have  demonstrated  the  existence  of 

19 


SIDE-LIGHTS    ON    ASTRONOMY 

objects  so  minute  that  they  find  their  way  among 
and  between  the  atoms  of  matter  as  rain-drops  do 
among  the  buildings  of  a  city.  More  wonderful  yet, 
it  seems  likely,  although  it  has  not  been  demonstrated, 
that  these  little  things,  called  "  corpuscles,"  play  an 
important  part  in  what  is  going  on  among  the  stars. 
Whether  this  be  true  or  not,  it  is  certain  that  there 
do  exist  in  the  universe  emanations  of  some  sort, 
producing  visible  effects,  the  investigation  of  which 
the  nineteenth  century  has  had  to  bequeath  to  the 
twentieth. 

For  the  purpose  of  the  navigator,  the  direction  of 
the  magnetic  needle  is  invariable  in  any  one  place, 
for  months  and  even  years ;  but  when  exact  scientific 
observations  on  it  are  made,  it  is  found  subject  to 
numerous  slight  changes.  The  most  regular  of  these 
consists  in  a  daily  change  of  its  direction.  It  moves 
one  way  from  morning  until  noon,  and  then,  late 
in  the  afternoon  and  during  the  night,  turns  back 
again  to  its  original  pointing.  The  laws  of  this  change 
have  been  carefully  studied  from  observations,  which 
show  that  it  is  least  at  the  equator  and  larger  as  we 
go  north  into  middle  latitudes;  but  no  explanation 
of  it  resting  on  an  indisputable  basis  has  ever  been 
offered. 

Besides  these  regular  changes,  there  are  others  of 
a  very  irregular  character.  Every  now  and  then  the 
changes  in  the  direction  of  the  magnet  are  wider  and 
more  rapid  than  those  which  occur  regularly  every 
day.  The  needle  may  move  back  and  forth  in  a 
way  so  fitful  as  to  show  the  action  of  some  unusual 
exciting  cause.  Such  movements  of  the  needle  are 
commonly  seen  when  there  is  a  brilliant  aurora. 
This  connection  shows  that  a  magnetic  storm  and 

20 


NEW  PROBLEMS  OF  THE  UNIVERSE 

an  aurora  must  be  due  to  the  same  or  some  connected 
causes. 

Those  of  us  who  are  acquainted  with  astronomical 
matters  know  that  the  number  of  spots  on  the  sun 
goes  through  a  regular  cycle  of  change,  having  a 
period  of  eleven  years  and  one  or  two  months.  Now, 
the  curious  fact  is,  when  the  number  and  violence  of 
magnetic  storms  are  recorded  and  compared,  it  is 
found  that  they  correspond  to  the  spots  on  the  sun, 
and  go  through  the  same  period  of  eleven  years. 
The  conclusion  seems  almost  inevitable:  magnetic 
storms  are  due  to  some  emanation  sent  out  by  the 
sun,  which  arises  from  the  same  cause  that  produces 
the  spots.  This  emanation  does  not  go  on  incessant- 
ly, but  only  in  an  occasional  way,  as  storms  follow 
each  other  on  the  earth.  What  is  it?  Every  at- 
tempt to  detect  it  has  been  in  vain.  Professor  Hale, 
at  the  Yerkes  Observatory,  has  had  in  operation  from 
time  to  time,  for  several  years,  his  ingenious  spectro- 
heliograph,  which  photographs  the  sun  by  a  single 
ray  of  the  spectrum.  This  instrument  shows  that 
violent  actions  are  going  on  in  the  sun,  which  ordinary 
observation  would  never  lead  us  to  suspect.  But  it 
has  failed  to  show  with  certainty  any  peculiar  emana- 
tion at  the  time  of  a  magnetic  storm  or  anything  con- 
nected with  such  a  storm. 

A  mystery  which  seems  yet  more  impenetrable  is 
associated  with  the  so-called  new  stars  which  blaze 
forth  from  time  to  time.  These  offer  to  our  sight 
the  most  astounding  phenomena  ever  presented  to 
the  physical  philosopher.  One  hundred  years  ago 
such  objects  offered  no  mystery.  There  was  no  rea- 
son to  suppose  that  the  Creator  of  the  universe  had 
ceased  His  functions;  and,  continuing  them,  it  was 

21 


SIDE-LIGHTS    ON    ASTRONOMY 

perfectly  natural  that  He  should  be  making  con- 
tinual additions  to  the  universe  of  stars.  But  the 
idea  that  these  objects  are  really  new  creations,  made 
out  of  nothing,  is  contrary  to  all  our  modern  ideas 
and  not  in  accord  with  the  observed  facts.  Grant- 
ing the  possibility  of  a  really  new  star — if  such  an 
object  were  created,  it  would  be  destined  to  take  its 
place  among  the  other  stars  as  a  permanent  member 
of  the  universe.  Instead  of  this,  such  objects  in- 
variably fade  away  after  a  few  months,  and  are 
changed  into  something  very  like  an  ordinary  nebula. 
A  question  of  transcendent  interest  is  that  of  the 
cause  of  these  outbursts.  It  cannot  be  said  that 
science  has,  up  to  the  present  time,  been  able  to  offer 
any  suggestion  not  open  to  question.  The  most  def- 
inite one  is  the  collision  theory,  according  to  which 
the  outburst  is  due  to  the  clashing  together  of  two 
stars,  one  or  both  of  which  might  previously  have 
been  dark,  like  a  planet.  The  stars  which  may  be 
actually  photographed  probably  exceed  one  hundred 
millions  in  number,  and  those  which  give  too  little 
light  to  affect  the  photographic  plate  may  be  vastly 
more  numerous  than  those  which  do.  Dark  stars 
revolve  around  bright  ones  in  an  infinite  variety  of 
ways,  and  complex  systems  of  bodies,  the  mem- 
bers of  which  powerfully  attract  each  other,  are  the 
rule  throughout  the  universe.  Moreover,  we  can  set 
no  limit  to  the  possible  number  of  dark  or  invisible 
stars  that  may  be  flying  through  the  celestial  spaces. 
While,  therefore,  we  cannot  regard  the  theory  of 
collision  as  established,  it  seems  to  be  the  only  one 
yet  put  forth  which  can  lay  any  claim  to  a  scientific 
basis.  What  gives  most  color  to  it  is  the  extreme 
suddenness  with  which  the  new  stars,  so  far  as  has 

22 


NEW    PROBLEMS    OF    THE    UNIVERSE 

yet  been  observed,  invariably  blaze  forth.  In  almost 
every  case  it  has  been  only  two  or  three  days  from 
the  time  that  the  existence  of  such  an  object  became 
known  until  it  had  attained  nearly  its  full  brightness. 
In  fact,  it  would  seem  that  in  the  case  of  the  star  in 
Perseus,  as  in  most  other  cases,  the  greater  part  of 
the  outburst  took  place  within  the  space  of  twenty- 
four  hours.  This  suddenness  and  rapidity  is  exactly 
what  would  be  the  result  of  a  collision. 

The  most  inexplicable  feature  of  all  is  the  rapid 
formation  of  a  nebula  around  this  star.  In  the  first 
photographs  of  the  latter,  the  appearance  presented 
is  simply  that  of  an  ordinary  star.  But,  in  the  course 
of  three  or  four  months,  the  delicate  photographs 
taken  at  the  Lick  Observatory  showed  that  a  nebu- 
lous light  surrounded  the  star,  and  was  continually 
growing  larger  and  larger.  At  first  sight,  there  would 
seem  to  be  nothing  extraordinary  in  this  fact.  Great 
masses  of  intensely  hot  vapor,  shining  by  their  own 
light,  would  naturally  be  thrown  out  from  the  star. 
Or,  if  the  star  had  originally  been  surrounded  by  a 
very  rare  nebulous  fog  or  vapor,  the  latter  would  be 
seen  by  the  brilliant  light  emitted  by  the  star.  On 
this  was  based  an  explanation  offered  by  Kapteyn, 
which  at  first  seemed  very  plausible.  It  was  that 
the  sudden  wave  of  light  thrown  out  by  the  star 
when  it  burst  forth  caused  the  illumination  of  the  sur- 
rounding vapor,  which,  though  really  at  rest,  would 
seem  to  expand  with  the  velocity  of  light,  as  the  illu- 
mination reached  more  and  more  distant  regions  of 
the  nebula.  This  result  may  be  made  the  subject  of 
exact  calculation.  The  velocity  of  light  is  such  as 
would  make  a  circuit  of  the  earth  more  than  seven 
times  in  a  second.  It  would,  therefore,  go  out  from 

3  23 


SIDE-LIGHTS    ON    ASTRONOMY 

the  star  at  the  rate  of  a  million  of  miles  in  between 
five  and  six  seconds.  In  the  lapse  of  one  of  our  days, 
the  light. would  have  filled  a  sphere  around  the  star 
having  a  diameter  more  than  one  hundred  and  fifty 
times  the  distance  of  the  sun  from  the  earth,  and 
more  than  five  times  the  dimensions  of  the  whole 
solar  system.  Continuing  its  course  and  enlarging 
its  sphere  day  after  day,  the  sight  presented  to  us 
would  have  been  that  of  a  gradually  expanding  nebu- 
lous mass — a  globe  of  faint  light  continually  increas- 
ing in  size  with  the  velocity  of  light. 

The  first  sentiment  the  reader  will  feel  on  this  sub- 
ject is  doubtless  one  of  surprise  that  the  distance  of 
the  star  should  be  so  great  as  this  explanation  would 
imply.  Six  months  after  the  explosion,  the  globe  of 
light,  as  actually  photographed,  was  of  a  size  which 
would  have  been  visible  to  the  naked  eye  only  as  a 
very  minute  object  in  the  sky.  Is  it  possible  that 
this  minute  object  could  have  been  thousands  of 
times  the  dimensions  of  our  solar  system? 

To  see  how  the  question  stands  from  this  point  of 
view,  we  must  have  some  idea  of  the  possible  distance 
of  the  new  star.  To  gain  this  idea,  we  must  find  some 
way  of  estimating  distances  in  the  universe.  For  a 
reason  which  will  soon  be  apparent,  we  begin  with 
the  greatest  structure  which  nature  offers  to  the  view 
of  man.  We  all  know  that  the  Milky  Way  is  formed 
of  countless  stars,  too  minute  to  be  individually  visi- 
ble to  the  naked  eye.  The  more  powerful  the  tele- 
scope through  which  we  sweep  the  heavens,  the 
greater  the  number  of  the  stars  that  can  be  seen  in  it. 
With  the  powerful  instruments  which  are  now  in  use 
for  photographing  the  sky,  the  number  of  stars 
brought  to  light  must  rise  into  the  hundreds  of 

24 


NEW    PROBLEMS    OF    THE    UNIVERSE 

millions,  and  the  greater  part  of  these  belong  to  the 
Milky  Way.  The  smaller  the  stars  we  count,  the 
greater  their  comparative  number  in  the  region  of 
the  Milky  Way.  Of  the  stars  visible  through  the 
telescope,  more  than  one-half  are  found  in  the  Milky 
Way,  which  may  be  regarded  as  a  girdle  spanning 
the  entire  visible  universe. 

Of  the  diameter  of  this  girdle  we  can  say,  almost 
with  certainty,  that  it  must  be  more  than  a  thousand 
times  as  great  as  the  distance  of  the  nearest  fixed  star 
from  us,  and  is  probably  two  or  three  times  greater. 
According  to  the  best  judgment  we  can  form,  our 
solar  system  is  situate  near  the  central  region  of  the 
girdle,  so  that  the  latter  must  be  distant  from  us 
by  half  its  diameter.  It  follows  that  if  we  can  im- 
agine a  gigantic  pair  of  compasses,  of  which  the 
points  extend  from  us  to  Alpha  Centauri,  the  nearest 
star,  we  should  have  to  measure  out  at  least  five 
hundred  spaces  with  the  compass,  and  perhaps  even 
one  thousand  or  more,  to  reach  the  region  of  the 
Milky  Way. 

With  this  we  have  to  connect  another  curious  fact. 
Of  eighteen  new  stars  which  have  been  observed  to 
blaze  forth  during  the  last  four  hundred  years,  all  are 
in  the  region  of  the  Milky  Way.  This  seems  to  show 
that,  as  a  rule,  they  belong  to  the  Milky  Way.  Ac- 
cepting this  very  plausible  conclusion,  the  new  star 
in  Perseus  must  have  been  more  than  five  hundred 
times  as  far  as  the  nearest  fixed  star.  We  know  that 
it  takes  light  four  years  to  reach  us  from  Alpha 
Centauri.  It  follows  that  the  new  star  was  at  a  dis- 
tance through  which  light  would  require  more  than 
two  thousand  years  to  travel,  and  quite  likely  a  time 
two  or  three  times  this.  It  requires  only  the  most 

25 


SIDE-LIGHTS    ON    ASTRONOMY 

elementary  ideas  of  geometry  to  see  that  if  we  sup- 
pose a  ray  of  light  to  shoot  from  a  star  at  such  a  dis- 
tance in  a  direction  perpendicular  to  the  line  of  sight 
from  us  to  the  star,  we  can  compute  how  fast  the  ray 
would  seem  to  us  to  travel.  Granting  the  distance 
to  be  only  two  thousand  light  years,  the  apparent 
size  of  the  sphere  around  the  star  which  the  light 
would  fill  at  the  end  of  one  year  after  the  explosion 
would  be  that  of  a  coin  seen  at  a  distance  of  two 
thousand  times  its  radius,  or  one  thousand  times  its 
diameter — say,  a  five-cent  piece  at  the  distance  of 
sixty  feet.  But,  as  a  matter  of  fact,  the  nebulous 
illumination  expanded  with  a  velocity  from  ten  to 
twenty  times  as  great  as  this. 

The  idea  that  the  nebulosity  around  the  new  star 
was  formed  by  the  illumination  caused  by  the  light 
of  the  explosion  spreading  out  on  all  sides  therefore 
fails  to  satisfy  us,  not  because  the  expansion  of  the 
nebula  seemed  to  be  so  slow,  but  because  it  was  many 
times  as  swift  as  the  speed  of  light.  Another  reason 
for  believing  that  it  was  not  a  mere  wave  of  light  is 
offered  by  the  fact  that  it  did  not  take  place  regularly 
in  every  direction  from  the  star,  but  seemed  to  shoot 
off  at  various  angles. 

Up  to  the  present  time,  the  speed  of  light  has  been 
to  science,  as  well  as  to  the  intelligence  of  our  race, 
almost  a  symbol  of  the  greatest  of  possible  speeds. 
The  more  carefully  we  reflect  on  the  case,  the  more 
clearly  we  shall  see  the  difficulty  in  supposing  any 
agency  to  travel  at  the  rate  of  the  seeming  emana- 
tions from  the  new  star  in  Perseus. 

As  the  emanation  is  seen  spreading  day  after  day, 
the  reader  may  inquire  whether  this  is  not  an  appear- 
ance due  to  some  other  cause  than  the  mere  motion 

26 


NEW  PROBLEMS  OF  THE  UNIVERSE 

of  light.  May  not  an  explosion  taking  place  in  the 
centre  of  a  star  produce  an  effect  which  shall  travel 
yet  faster  than  light?  We  can  only  reply  that  no 
such  agency  is  known  to  science. 

But  is  there  really  anything  intrinsically  improb- 
able in  an  agency  travelling  with  a  speed  many  times 
that  of  light?  In  considering  that  there  is,  we  may 
fall  into  an  error  very  much  like  that  into  which  our 
predecessors  fell  in  thinking  it  entirely  out  of  the 
range  of  reasonable  probability  that  the  stars  should 
be  placed  at  such  distances  as  we  now  know  them 
to  be. 

Accepting  it  as  a  fact  that  agencies  do  exist  which 
travel  from  sun  to  planet  and  from  star  to  star  with 
a  speed  which  beggars  all  our  previous  ideas,  the 
first  question  that  arises  is  that  of  their  nature  and 
mode  of  action.  This  question  is,  up  to  the  present 
time,  one  which  we  do  not  see  any  way  of  completely 
answering.  The  first  difficulty  is  that  we  have  no 
evidence  of  these  agents  except  that  afforded  by  their 
action.  We  see  that  the  sun  goes  through  a  regular 
course  of  pulsations,  each  requiring  eleven  years  for 
completion;  and  we  see  that,  simultaneously  with 
these,  the  earth's  magnetism  goes  through  a  similar 
course  of  pulsations.  The  connection  of  the  two, 
therefore,  seems  absolutely  proven.  But  when  we 
ask  by  what  agency  it  is  possible  for  the  sun  to  affect 
the  magnetism  of  the  earth,  and  when  we  trace  the 
passage  of  some  agent  between  the  two  bodies,  we 
find  nothing  to  explain  the  action.  To  all  appear- 
ance, the  space  between  the  earth  and  the  sun  is  a 
perfect  void.  That  electricity  cannot  of  itself  pass 
through  a  vacuum  seems  to  be  a  well-established  law 
of  physics.  It  is  true  that  electromagnetic  waves, 

27 


SIDE-LIGHTS    ON    ASTRONOMY 

which  are  supposed  to  be  of  the  same  nature  with 
those  of  light,  and  which  are  used  in  wireless  teleg- 
raphy, do  pass  through  a  vacuum  and  may  pass 
from  the  sun  to  the  earth.  But  there  is  no  way  of 
explaining  how  such  waves  would  either  produce  or 
affect  the  magnetism  of  the  earth. 

The  mysterious  emanations  from  various  sub- 
stances, under  certain  conditions,  may  have  an  in- 
timate relation  with  yet  another  of  the  mysteries  of 
the  universe.  It  is  a  fundamental  law  of  the  uni- 
verse that  when  a  body  emits  light  or  heat,  or  any- 
thing capable  of  being  transformed  into  light  or  heat, 
it  can  do  so  only  by  the  expenditure  of  force,  limited 
in  supply.  The  sun  and  stars  are  continually  send- 
ing out  a  flood  of  heat.  They  are  exhausting  the  in- 
ternal supply  of  something  which  must  be  limited  in 
extent.  Whence  comes  the  supply?  How  is  the 
heat  of  the  sun  kept  up  ?  If  it  were  a  hot  body  cool- 
ing off,  a  very  few  years  would  suffice  for  it  to  cool 
off  so  far  that  its  surface  would  become  solid  and  very 
soon  cold.  In  recent  years,  the  theory  universally 
accepted  has  been  that  the  supply  of  heat  is  kept  up 
by  the  continual  contraction  of  the  sun,  by  mutual 
gravitation  of  its  parts  as  it  cools  off.  This  theory 
has  the  advantage  of  enabling  us  to  calculate,  with 
some  approximation  to  exactness,  at  what  rate  the 
sun  must  be  contracting  in  order  to  keep  up  the 
supply  of  heat  which  it  radiates.  On  this  theory, 
it  must,  ten  millions  of  years  ago,  have  had  twice 
its  present  diameter,  while  less  than  twenty  mill- 
ions of  years  ago  it  could  not  have  existed  except 
as  an  immense  nebula  rilling  the  whole  solar  system. 
We  must  bear  in  mind  that  this  theory  is  the  only 
one  which  accounts  for  the  supply  of  heat,  even 

28 


NEW    PROBLEMS    OF    THE    UNIVERSE 

through  human  history.  If  it  be  true,  then  the  sun, 
earth,  and  solar  system  must  be  less  than  twenty 
million  years  old. 

Here  the  geologists  step  in  and  tell  us  that  this 
conclusion  is  wholly  inadmissible.  The  study  of  the 
strata  of  the  earth  and  of  many  other  geological 
phenomena,  they  assure  us,  makes  it  certain  that  the 
earth  must  have  existed  much  in  its  present  condi- 
tion for  hundreds  of  millions  of  years.  During  all 
that  time  there  can  have  been  no  great  diminution 
in  the  supply  of  heat  radiated  by  the  sun. 

The  astronomer,  in  considering  this  argument,  has 
to  admit  that  he  finds  a  similar  difficulty  in  connec- 
tion with  the  stars  and  nebulae.  It  is  an  impossibility 
to  regard  these  objects  as  new;  they  must  be  as  old 
as  the  universe  itself.  They  radiate  heat  and  light 
year  after  year.  In  all  probability,  they  must  have 
been  doing  so  for  millions  of  years.  Whence  comes 
the  supply  ?  The  geologist  may  well  claim  that  un- 
til the  astronomer  explains  this  mystery  in  his  own 
domain,  he  cannot  declare  the  conclusions  of  geology 
as  to  the  age  of  the  earth  to  be  wholly  inadmissible. 

Now,  the  scientific  experiments  of  the  last  two 
years  have  brought  this  mystery  of  the  celestial  spaces 
right  down  into  our  earthly  laboratories.  M.  and 
Madame  Curie  have  discovered  the  singular  metal 
radium,  which  seems  to  send  out  light,  heat,  and 
other  rays  incessantly,  without,  so  far  as  has  yet  been 
determined,  drawing  the  required  energy  from  any 
outward  source.  As  we  have  already  pointed  out, 
such  an  emanation  must  come  from  some  storehouse 
of  energy.  Is  the  storehouse,  then,  in  the  medium 
itself,  or  does  the  latter  draw  it  from  surrounding 
objects  ?  If  it  does,  it  must  abstract  heat  from  these 

29 


SIDE-LIGHTS    ON    ASTRONOMY 

objects.  This  question  has  been  settled  by  Pro- 
fessor Dewar,  at  the  Royal  Institution,  London,  by 
placing  the  radium  in  a  medium  next  to  the  coldest 
that  art  has  yet  produced — liquid  air.  The  latter  is 
surrounded  by  the  only  yet  colder  medium,  liquid 
hydrogen,  so  that  no  heat  can  reach  it.  Under  these 
circumstances,  the  radium  still  gives  out  heat,  boiling 
away  the  liquid  air  until  the  latter  has  entirely  dis- 
appeared. Instead  of  the  radiation  diminishing  with 
time,  it  rather  seems  to  increase. 

Called  on  to  explain  all  this,  science  can  only  say 
that  a  molecular  change  must  be  going  on  in  the 
radium,  to  correspond  to  the  heat  it  gives  out.  What 
that  change  may  be  is  still  a  complete  mystery.  It 
is  a  mystery  which  we  find  alike  in  those  minute 
specimens  of  the  rarest  of  substances  under  our 
microscopes,  in  the  sun,  and  in  the  vast  nebulous 
masses  in  the  midst  of  which  our  whole  solar  system 
would  be  but  a  speck.  The  unravelling  of  this  mys- 
tery must  be  the  great  work  of  science  of  the  twen- 
tieth century.  What  results  shall  follow  for  man- 
kind one  cannot  say,  any  more  than  he  could  have 
said  two  hundred  years  ago  what  modern  science 
would  bring  forth.  Perhaps,  before  future  develop- 
ments, all  the  boasted  achievements  of  the  nineteenth 
century  may  take  the  modest  place  which  we  now 
assign  to  the  science  of  the  eighteenth  century — that 
of  the  infant  which  is  to  grow  into  a  man. 


Ill 

THE   STRUCTURE   OF   THE   UNIVERSE 

THE  questions  of  the  extent  of  the  universe  in 
space  and  of  its  duration  in  time,  especially  of 
its  possible  infinity  in  either  space  or  time,  are  of  the 
highest  interest  both  in  philosophy  and  science.  The 
traditional  philosophy  had  no  means  of  attacking 
these  questions  except  considerations  suggested  by 
pure  reason,  analogy,  and  that  general  fitness  of 
things  which  was  supposed  to  mark  the  order  of 
nature.  With  modern  science  the  questions  belong 
to  the  realm  of  fact,  and  can  be  decided  only  by  the 
results  of  observation  and  a  study  of  the  laws  to 
which  these  results  may  lead. 

From  the  philosophic  stand-point,  a  discussion  of 
this  subject  which  is  of  such  weight  that  in  the  his- 
tory of  thought  it  must  be  assigned  a  place  above 
all  others,  is  that  of  Kant  in  his  Kritik.  Here  we 
find  two  opposing  propositions — the  thesis  that  the 
universe  occupies  only  a  finite  space  and  is  of  finite 
duration;  the  antithesis  that  it  is  infinite  both  as  re- 
gards extent  in  space  and  duration  in  time.  Both  of 
these  opposing  propositions  are  shown  to  admit  of 
demonstration  with  equal  force,  not  directly,  but 
by  the  methods  of  reductio  ad  absurdum.  The 
difficulty,  discussed  by  Kant,  was  more  tersely  ex- 
pressed by  Hamilton  in  pointing  out  that  we  could 

31 


SIDE-LIGHTS    ON    ASTRONOMY 

neither  conceive  of  infinite  space  nor  of  space  as 
bounded. 

The  methods  and  conclusions  of  modern  astronomy 
are,  however,  in  no  way  at  variance  with  Kant's  rea- 
soning, so  far  as  it  extends.  The  fact  is  that  the  prob- 
lem with  which  the  philosopher  of  Konigsberg  vainly 
grappled  is  one  which  our  science  cannot  solve  any 
more  than  could  his  logic.  We  may  hope  to  gain 
complete  information  as  to  everything  which  lies 
within  the  range  of  the  telescope,  and  to  trace  to  its 
beginning  every  process  which  we  can  now  see  going 
on  in  space.  But  before  questions  of  the  absolute 
beginning  of  things,  or  of  the  boundary  beyond  which 
nothing  exists,  our  means  of  inquiry  are  quite  pow- 
erless. 

Another  example  of  the  ancient  method  is  found  in 
the  great  work  of  Copernicus.  It  is  remarkable  how 
completely  the  first  expounder  of  the  system  of  the 
world  was  dominated  by  the  philosophy  of  his  time, 
which  he  had  inherited  from,  his  predecessors.  This  is 
seen  not  only  in  the  general  course  of  thought  through 
the  opening  chapters  of  his  work,  but  among  his  in- 
troductory propositions.  The  first  of  these  is  that  the 
universe — mundus — as  well  as  the  earth,  is  spherical 
in  form.  His  arguments  for  the  sphericity  of  the 
earth,  as  derived  from  observation,  are  little  more 
than  a  repetition  of  those  of  Ptolemy,  and  therefore 
not  of  special  interest.  His  proposition  that  the 
universe  is  spherical  is,  however,  not  based  on  obser- 
vation, but  on  considerations  of  the  perfection  of  the 
spherical  form,  the  general  tendency  of  bodies — a 
drop  of  water,  for  example — to  assume  this  form,  and 
the  sphericity  of  the  sun  and  moon.  The  idea  re- 
tained its  place  in  his  mind,  although  the  funda- 

32 


THE    ST.RUCTURE    OF    THE    UNIVERSE 

mental  conception  of  his  system  did  away  with  the 
idea  of  the  universe  having  any  well-defined  form. 

The  question  as  attacked  by  modern  astronomy  is 
this:  we  see  scattered  through  space  in  every  direc- 
tion many  millions  of  stars  of  various  orders  of  bright- 
ness and  at  distances  so  great  as  to  defy  exact  meas- 
urement, except  in  the  case  of  a  few  of  the  nearest. 
Has  this  collection  of  stars  any  well-defined  boun- 
dary, or  is  what  we  see  merely  that  part  of  an  infinite 
mass  which  chances  to  lie  within  the  range  of  our 
telescopes  ?  If  we  were  transported  to  the  most  dis- 
tant star  of  which  we  have  knowledge,  should  we 
there  find  ourselves  still  surrounded  by  stars  on  all 
sides,  or  would  the  space  beyond  be  void?  Grant- 
ing that,  in  any  or  every  direction,  there  is  a  limit  to 
the  universe,  and  that  the  space  beyond  is  therefore 
void,  what  is  the  form  of  the  whole  system  and  the 
distance  of  its  boundaries  ?  Preliminary  in  some  sort 
to  these  questions  are  the  more  approachable  ones: 
Of  what  sort  of  matter  is  the  universe  formed?  and 
into  what  sort  of  bodies  is  this  matter  collected  ? 

To  the  ancients  the  celestial  sphere  was  a  reality, 
instead  of  a  mere  effect  of  perspective,  as  we  regard 
it.  The  stars  were  set  on  its  surface,  or  at  least  at 
no  great  distance  within  its  crystalline  mass.  Out- 
side of  it  imagination  placed  the  empyrean.  When 
and  how  these  conceptions  vanished  from  the  mind 
of  man,  it  would  be  as  hard  to  say  as  when  and  how 
Santa  Claus  gets  transformed  in  the  mind  of  the 
child.  They  are  not  treated  as  realities  by  any  astro- 
nomical writer  from  Ptolemy  down;  yet,  the  im- 
pressions and  forms  of  thought  to  which  they  gave 
rise  are  well  marked  in  Copernicus  and  faintly  evi- 
dent in  Kepler.  The  latter  was  perhaps  the  first  to 

33 


SIDE-LIGHTS    ON    ASTRONOMY 

suggest  that  the  sun  might  be  one  of  the  stars;  yet, 
from  defective  knowledge  of  the  relative  brightness 
of  the  latter,  he  was  led  to  the  conclusion  that  their 
distances  from  each  other  were  less  than  the  distance 
which  separated  them  from  the  sun.  The  latter  he 
supposed  to  stand  in  the  centre  of  a  vast  vacant 
region  within  the  system  of  stars. 

For  us  the  great  collection  of  millions  of  stars 
which  are  made  known  to  us  by  the  telescope,  to- 
gether with  all  the  invisible  bodies  which  may  be  con- 
tained within  the  limits  of  the  system,  form  the  uni- 
verse. Here  the  term  "universe"  is  perhaps  ob- 
jectionable because  there  may  be  other  systems  than 
the  one  with  which  we  are  acquainted.  The  term 
stellar  system  is,  therefore,  a  better  one  by  which  to 
designate  the  collection  of  stars  in  question. 

It  is  remarkable  that  the  first  known  propounder 
of  that  theory  of  the  form  and  arrangement  of  the 
system  which  has  been  most  generally  accepted 
seems  to  have  been  a  writer  otherwise  unknown  in 
science — Thomas  Wright,  of  Durham,  England.  He 
is  said  to  have  published  a  book  on  the  theory  of 
the  universe,  about  1750.  It  does  not  appear  that 
this  work  was  of  a  very  scientific  character,  and  it 
was,  perhaps,  too  much  in  the  nature  of  a  speculation 
to  excite  notice  in  scientific  circles.  One  of  the 
curious  features  of  the  history  is  that  it  was  Kant 
who  first  cited  Wright's  theory,  pointed  out  its  ac- 
cordance with  the  appearance  of  the  Milky  Way,  and 
showed  its  general  reasonableness.  But,  at  the  time 
in  question,  the  work  of  the  philosopher  of  Konigs- 
berg  seems  to  have  excited  no  more  notice  among  his 
scientific  contemporaries  than  that  of  Wright. 

Kant's  fame  as  a  speculative  philosopher  has  so 

34 


THE  STRUCTURE  OF  THE  UNIVERSE 

eclipsed  his  scientific  work  that  the  latter  has  but 
recently  been  appraised  at  its  true  value.  He  was 
the  originator  of  views  which,  though  defective  in 
detail,  embodied  a  remarkable  number  of  the  results 
of  recent  research  on  the  structure  and  form  of  the 
universe,  and  the  changes  taking  place  in  it.  The 
most  curious  illustration  of  the  way  in  which  he  ar- 
rived at  a  correct  conclusion  by  defective  reasoning 
is  found  in  his  anticipation  of  the  modern  theory  of 
a  constant  retardation  of  the  velocity  with  which  the 
earth  revolves  on  its  axis.  He  conceived  that  this 
effect  must  result  from  the  force  exerted  by  the  tidal 
wave,  as  moving  towards  the  west  it  strikes  the 
eastern  coasts  of  Asia  and  America.  An  opposite 
conclusion  was  reached  by  Laplace,  who  showed  that 
the  effect  of  this  force  was  neutralized  by  forces  pro- 
ducing the  wave  and  acting  in  the  opposite  direction. 
And  yet,  nearly  a  century  later,  it  was  shown  that 
while  Laplace  was  quite  correct  as  regards  the  gen- 
eral principles  involved,  the  friction  of  the  moving 
water  must  prevent  the  complete  neutralization  of 
the  two  opposing  forces,  and  leave  a  small  residual 
force  acting  towards  the  west  and  retarding  the 
rotation.  Kant's  conclusion  was  established,  but  by 
an  action  different  from  that  which  he  supposed. 

The  theory  of  Wright  and  Kant,  which  was  still 
further  developed  by  Herschel,  was  that  our  stellar 
system  has  somewhat  the  form  of  a  flattened  cylinder, 
or  perhaps  that  which  the  earth  would  assume  if,  in 
consequence  of  more  rapid  rotation,  the  bulging  out 
at  its  equator  and  the  flattening  at  its  poles  were 
carried  to  an  extreme  limit.  This  form  has  been 
correctly  though  satirically  compared  to  that  of  a 
grindstone.  It  rests  to  a  certain  extent,  but  not 

35 


SIDE-LIGHTS    ON    ASTRONOMY 

entirely,  on  the  idea  that  the  stars  are  scattered 
through  space  with  equal  thickness  in  every  direc- 
tion, and  that  the  appearance  of  the  Milky  Way  is 
due  to  the  fact  that  we,  situated  in  the  centre  of  this 
flattened  system,  see  more  stars  in  the  direction  of 
the  circumference  of  the  system  than  in  that  of  its 
poles.  The  argument  on  which  the  view  in  question 
rests  may  be  made  clear  in  the  following  way. 

Let  us  chose  for  our  observations  that  hour  of  the 
night  at  which  the  Milky  Way  skirts  our  horizon. 
This  is  nearly  the  case  in  the  evenings  of  May  and 
June,  though  the  coincidence  with  the  horizon  can 
never  be  exact  except  to  observers  stationed  near 
the  tropics.  Using  the  figure  of  the  grindstone,  we 
at  its  centre  will  then  have  its  circumference  around 
our  horizon,  while  the  axis  will  be  nearly  vertical. 
The  points  in  which  the  latter  intersects  the  celestial 
sphere  are  called  the  galactic  poles.  There  will  be 
two  of  these  poles,  the  one  at  the  hour  in  question 
near  the  zenith,  the  other  in  our  nadir,  and  therefore 
invisible  to  us,  though  seen  by  our  antipodes.  Our 
horizon  corresponds,  as  it  were,  to  the  central  circle 
of  the  Milky  Way,  which  now  surrounds  us  on  all 
sides  in  a  horizontal  direction,  while  the  galactic  poles 
are  90°  distant  from  every  part  of  it,  as  every  point 
of  the  horizon  is  90°  from  the  zenith. 

Let  us  next  count  the  number  of  stars  visible  in  a 
powerful  telescope  in  the  region  of  the  heavens  around 
the  galactic  pole,  now  our  zenith,  and  find  the  aver- 
age number  per  square  degree.  This  will  be  the 
richness  of  the  region  in  stars.  Then  we  take  regions 
nearer  the  horizontal  Milky  Way — say  that  contained 
between  10°  and  20°  from  the  zenith — and,  by  a  simi- 
lar count,  find  its  richness  in  stars.  We  do  the  same 

36 


THE    STRUCTURE    OF    THE    UNIVERSE 

for  other  regions,  nearer  and  nearer  to  the  horizon, 
till  we  reach  the  galaxy  itself.  The  result  of  all  the 
counts  will  be  that  the  richness  of  the  sky  in  stars 
is  least  around  the  galactic  pole,  and  increases  in 
every  direction  towards  the  Milky  Way. 

Without  such  counts  of  the  stars  we  might  imagine 
our  stellar  system  to  be  a  globular  collection  of  stars 
around  which  the  object  in  question  passed  as  a  gir- 
dle; and  we  might  take  a  globe  with  a  chain  passing 
around  it  as  representative  of  the  possible  figure  of 
the  stellar  system.  But  the  actual  increase  in  star- 
thickness  which  we  have  pointed  out  shows  us  that 
this  view  is  incorrect.  The  nature  and  validity  of 
the  conclusions  to  be  drawn  can  be  best  appreciated 
by  a  statement  of  some  features  of  this  tendency  of 
the  stars  to  crowd  towards  the  galactic  circle. 

Most  remarkable  is  the  fact  that  the  tendency  is 
seen  even  among  the  brighter  stars.  Without  either 
telescope  or  technical  knowledge,  the  careful  observer 
of  the  stars  will  notice  that  the  most  brilliant  con- 
stellations show  this  tendency.  The  glorious  Orion, 
Canis  Major  containing  the  brightest  star  in  the 
heavens,  Cassiopeia,  Perseus,  Cygnus,  and  Lyra  with 
its  bright-blue  Vega,  not  to  mention  such  constella- 
tions as  the  Southern  Cross,  all  lie  in  or  near  the 
Milky  Way.  Schiaparelli  has  extended  the  investi- 
gation to  all  the  stars  visible  to  the  naked  eye.  He 
laid  down  on  planispheres  the  number  of  such  stars 
in  each  region  of  the  heavens  of  5°  square.  Each 
region  was  then  shaded  with  a  tint  that  was  darker 
as  the  region  was  richer  in  stars.  The  very  existence 
of  the  Milky  Way  was  ignored  in  this  work,  though 
his  most  darkly  shaded  regions  lie  along  the  course 
of  this  belt.  By  drawing  a  band  around  the  sky  so 

37 


SIDE-LIGHTS    ON    ASTRONOMY 

as  to  follow  or  cover  his  darkest  regions,  we  shall  re- 
discover the  course  of  the  Milky  Way  without  any 
reference  to  the  actual  object.  It  is  hardly  neces- 
sary to  add  that  this  result  would  be  reached  with 
yet  greater  precision  if  we  included  the  telescopic 
stars  to  any  degree  of  magnitude — plotting  them  on 
a  chart  and  shading  the  chart  in  the  same  way. 
What  we  learn  from  this  is  that  the  stellar  system  is 
not  an  irregular  chaos;  and  that  notwithstanding  all 
its  minor  irregularities,  it  may  be  considered  as  built 
up  with  special  reference  to  the  Milky  Way  as  a  foun- 
dation. 

Another  feature  of  the  tendency  in  question  is  that 
it  is  more  and  more  marked  as  we  include  fainter 
stars  in  our  count.  The  galactic  region  is  perhaps 
twice  as  rich  in  stars  visible  to  the  naked  eye  as  the 
rest  of  the  heavens.  In  telescopic  stars  to  the  ninth 
magnitude  it  is  three  or  four  times  as  rich,  In  the 
stars  found  on  the  photographs  of  the  sky  made  at 
the  Harvard  and  other  observatories,  and  in  the  star- 
gauges  of  the  Herschels,  it  is  from  five  to  ten  times 
as  rich. 

Another  feature  showing  the  unity  of  the  system 
is  the  symmetry  of  the  heavens  on  the  two  sides  of 
the  galactic  belt.  Let  us  return  to  our  supposition 
of  such  a  position  of  the  celestial  sphere,  with  respect 
to  the  horizon,  that  the  latter  coincides  with  the  cen- 
tral line  of  this  belt,  one  galactic  pole  being  near  our 
zenith.  The  celestial  hemisphere  which,  being  above 
our  horizon,  is  visible  to  us,  is  the  one  to  which  we 
have  hitherto  directed  our  attention  in  describing 
the  distribution  of  the  stars.  But  below  our  horizon 
is  another  hemisphere,  that  of  our  antipodes,  which 
is  the  counterpart  of  ours.  The  stars  which  it  con- 

38 


THE  STRUCTURE  OF  THE  UNIVERSE 

tains  are  in  a  different  part  of  the  universe  from  those 
which  we  see,  and,  without  unity  of  plan,  would  not 
be  subject  to  the  same  law.  But  the  most  accurate 
counts  of  stars  that  have  been  made  fail  to  show  any 
difference  in  their  general  arrangement  in  the  two 
hemispheres.  They  are  just  as  thick  around  the 
south  galactic  poles  as  around  the  north  one.  They 
show  the  same  tendency  to  crowd  towards  the  Milky 
Way  in  the  hemisphere  invisible  to  us  as  in  the  hemi- 
sphere which  we  see.  Slight  differences  and  irregu- 
larities, are,  indeed,  found  in  the  enumeration,  but 
they  are  no  greater  than  must  necessarily  arise  from 
the  difficulty  of  stopping  our  count  at  a  perfectly 
fixed  magnitude.  The  aim  of  star-counts  is  not  to 
estimate  the  total  number  of  stars,  for  this  is  beyond 
our  power,  but  the  number  visible  with  a  given  tele- 
scope. In  such  work  different  observers  have  ex- 
plored different  parts  of  the  sky,  and  in  a  count  of 
the  same  region  by  two  observers  we  shall  find  that, 
although  they  attempt  to  stop  at  the  same  magni- 
tude, each  will  include  a  great  number  of  stars  which 
the  other  omits.  There  is,  therefore,  room  for  con- 
siderable difference  in  the  numbers  of  stars  recorded, 
without  there  being  any  actual  inequality  between 
the  two  hemispheres. 

A  corresponding  similarity  is  found  in  the  physical 
constitution  of  the  stars  as  brought  out  by  the 
spectroscope.  The  Milky  Way  is  extremely  rich  in 
bluish  stars,  which  make  up  a  considerable  majority 
of  the  cloudlike  masses  there  seen.  But  when  we 
recede  from  the  galaxy  on  one  side,  we  find  the  blue 
stars  becoming  thinner,  while  those  having  a  yellow 
tinge  become  relatively  more  numerous.  This  dif- 
ference of  color  also  is  the  same  on  the  two  sides  of 
4  39 


SIDE-LIGHTS    ON    ASTRONOMY 

the  galactic  plane.  Nor  can  any  systematic  differ- 
ence be  detected  between  the  proper  motions  of  the 
stars  in  these  two  hemispheres.  If  the  largest  known 
proper  motion  is  found  in  the  one,  the  second  largest 
is  in  the  other.  Counting  all  the  known  stars  that 
have  proper  motions  exceeding  a  given  limit,  we  find 
about  as  many  in  one  hemisphere  as  in  the  other. 
In  this  respect,  also,  the  universe  appears  to  be  alike 
through  its  whole  extent.  It  is  the  uniformity  thus 
prevailing  through  the  visible  universe,  as  far  as  we 
can  see,  in  two  opposite  directions,  which  inspires  us 
with  confidence  in  the  possibility  of  ultimately  reach- 
ing some  well-founded  conclusion  as  to  the  extent  and 
structure  of  the  system. 

All  these  facts  concur  in  supporting  the  view  of 
Wright,  Kant,  and  Herschel  as  to  the  form  of  the 
universe.  The  farther  out  the  stars  extend  in  any 
direction,  the  more  stars  we  may  see  in  that  direction. 
In  the  direction  of  the  axis  of  the  cylinder,  the  dis- 
tances of  the  boundary  are  least,  so  that  we  see  fewer 
stars.  The  farther  we  direct  our  attention  towards 
the  equatorial  regions  of  the  system,  the  greater  the 
distance  from  us  to  the  boundary,  and  hence  the 
more  stars  we  see.  The  fact  that  the  increase  in  the 
number  of  stars  seen  towards  the  equatorial  region 
of  the  system  is  greater,  the  smaller  the  stars,  is  the 
natural  consequence  of  the  fact  that  distant  stars 
come  within  our  view  in  greater  numbers  towards  the 
equatorial  than  towards  the  polar  regions. 

Objections  have  been  raised  to  the  Herschelian 
view  on  the  ground  that  it  assumes  an  approximately 
uniform  distribution  of  the  stars  in  space.  It  has 
been  claimed  that  the  fact  of  our  seeing  more  stars 
in  one  direction  than  in  another  may  not  arise  merely 

40 


THE  STRUCTURE  OF  THE  UNIVERSE 

from  our  looking  through  a  deeper  stratum,  as  Her- 
schel  supposed,  but  may  as  well  be  due  to  the  stars 
being  more  thinly  scattered  in  the  direction  of  the 
axis  of  the  system  than  in  that  of  its  equatorial  region. 
The  great  inequalities  in  the  richness  of  neighboring 
regions  in  the  Milky  Way  show  that  the  hypothesis 
of  uniform  distribution  does  not  apply  to  the  equa- 
torial region.  The  claim  has  therefore  been  made 
that  there  is  no  proof  of  the  system  extending  out 
any  farther  in  the  equatorial  than  in  the  polar  di- 
rection. 

The  consideration  of  this  objection  requires  a 
closer  inquiry  as  to  what  we  are  to  understand  by 
the  form  of  our  system.  We  have  already  pointed 
out  the  impossibility  of  assigning  any  boundary  be- 
yond which  we  can  say  that  nothing  exists.  And 
even  as  regards  a  boundary  of  our  stellar  system,  it 
is  impossible  for  us  to  assign  any  exact  limit  beyond 
which  no  star  is  visible  to  us.  The  analogy  of  col- 
lections of  stars  seen  in  various  parts  of  the  heavens 
leads  us  to  suppose  that  there  may  be  no  well-defined 
form  to  our  system,  but  that,  as  we  go  out  farther 
and  farther,  we  shall  see  occasional  scattered  stars 
to,  possibly,  an  indefinite  distance.  The  truth  prob- 
ably is  that,  as  in  ascending  a  mountain,  we  find  the 
trees,  which  may  be  very  dense  at  its  base,  thin  out 
gradually  as  we  approach  the  summit,  where  there 
may  be  few  or  none,  so  we  might  find  the  stars  to 
thin  out  could  we  fly  to  the  distant  regions  of  space. 
The  practical  question  is  whether,  in  such  a  flight, 
we  should  find  this  sooner  by  going  in  the  direction  of 
the  axis  of  our  system  than  by  directing  our  course 
towards  the  Milky  Way.  If  a  point  is  at  length 
reached  beyond  which  there  are  but  few  scattered 

41 


SIDE-LIGHTS    ON    ASTRONOMY 

stars,  such  a  point  would,  for  us,  mark  the  boundary 
of  our  system.  From  this  point  of  view  the  answer 
does  not  seem  to  admit  of  doubt.  If,  going  in  every 
direction,  we  mark  the  point,  if  any,  at  which  the 
great  mass  of  the  stars  are  seen  behind  us,  the  total- 
ity of  all  these  points  will  lie  on  a  surface  of  the  gen- 
eral form  that  Herschel  supposed. 

There  is  still  another  direct  indication  of  the  fini- 
tude  of  our  stellar  system  upon  which  we  have  not 
touched.  If  this  system  extended  out  without  limit 
in  any  direction  whatever,  it  is  shown  by  a  geometric 
process  which  it  is  not  necessary  to  explain  in  the 
present  connection,  but  which  is  of  the  character  of 
mathematical  demonstration,  that  the  heavens  would, 
in  every  direction  where  this  was  true,  blaze  with  the 
light  of  the  noonday  sun.  This  would  be  very  differ- 
ent from  the  blue-black  sky  which  we  actually  see 
on  a  clear  night,  and  which,  with  a  reservation  that 
we  shall  consider  hereafter,  shows  that,  how  far  so- 
ever our  stellar  system  may  extend,  it  is  not  infinite. 
Beyond  this  negative  conclusion  the  fact  does  not 
teach  us  much.  Vast,  indeed,  is  the  distance  to 
which  the  system  might  extend  without  the  sky  ap- 
pearing much  brighter  than  it  is,  and  we  must  have 
recourse  to  other  considerations  in  seeking  for  in- 
dications of  a  boundary,  or  even  of  a  well-marked 
thinning  out,  of  stars. 

If,  as  was  formerly  supposed,  the  stars  did  not 
greatly  differ  in  the  amount  of  light  emitted  by  each, 
and  if  their  diversity  of  apparent  magnitude  were  due 
principally  to  the  greater  distance  of  the  fainter  stars, 
then  the  brightness  of  a  star  would  enable  us  to  form 
a  more  or  less  approximate  idea  of  its  distance.  But 
the  accumulated  researches  of  the  past  seventy  years 

42 


THE  STRUCTURE  OF  THE  UNIVERSE 

show  that  the  stars  differ  so  enormously  in  their 
actual  luminosity  that  the  apparent  brightness  of  a 
star  affords  us  only  a  very  imperfect  indication  of  its 
distance.  While,  in  the  general  average,  the  brighter 
stars  must  be  nearer  to  us  than  the  fainter  ones,  it 
by  no  means  follows  that  a  very  bright  star,  even  of 
the  first  magnitude,  is  among  the  nearer  to  our  sys- 
tem. Two  stars  are  worthy  of  especial  mention  in 
this  connection,  Canopus  and  Rigel.  The  first  is, 
with  the  single  exception  of  Sinus,  the  brightest  star 
in  the  heavens.  The  other  is  a  star  of  the  first 
magnitude  in  the  southwest  corner  of  Orion.  The 
most  long-continued  and  complete  measures  of  par- 
allax yet  made  are  those  carried  on  by  Gill,  at  the 
Cape  of  Good  Hope,  on  these  two  and  some  other 
bright  stars.  The  results,  published  in  1901,  show 
that  neither  of  these  bodies  has  any  parallax  that 
can  be  measured  by  the  most  refined  instrumental 
means  known  to  astronomy.  In  other  words,  the 
distance  of  these  stars  is  immeasurably  great.  The 
actual  amount  of  light  emitted  by  each  is  certainly 
thousands  and  probably  tens  of  thousands  of  times 
that  of  the  sun. 

Notwithstanding  the  difficulties  that  surround  the 
subject,  we  can  at  least  say  something  of  the  distance 
of  a  considerable  number  of  the  stars.  Two  methods 
are  available  for  our  estimate — measures  of  parallax 
and  determination  of  proper  motions. 

The  problem  of  stellar  parallax,  simple  though  it 
is  in  its  conception,  is  the  most  delicate  and  difficult 
of  all  which  the  practical  astronomer  has  to  encounter. 
An  idea  of  it  may  be  gained  by  supposing  a  minute 
object  on  a  mountain-top,  we  know  not  how  many 
miles  away,  to  be  visible  through  a  telescope.  The 

43 


SIDE-LIGHTS    ON    ASTRONOMY 

observer  is  allowed  to  change  the  position  of  his  in- 
strument by  two  inches,  but  no  more.  He  is  re- 
quired to  determine  the  change  in  the  direction  of 
the  object  produced  by  this  minute  displacement 
with  accuracy  enough  to  determine  the  distance  of 
the  mountain.  This  is  quite  analogous  to  the  de- 
termination of  the  change  in  the  direction  in  which 
we  see  a  star  as  the  earth,  moving  through  its  vast 
circuit,  passes  from  one  extremity  of  its  orbit  to  the 
other.  Representing  this  motion  on  such  a  scale 
that  the  distance  of  our  planet  from  the  sun  shall 
be  one  inch,  we  find  that  the  nearest  star,  on  the 
same  scale,  will  be  more  than  four  miles  away,  and 
scarcely  one  out  of  a  million  will  be  at  a  less  distance 
than  ten  miles.  It  is  only  by  the  most  wonderful 
perfection  both  in  the  heliometer,  the  instrument 
principally  used  for  these  measures,  and  in  methods 
of  observation,  that  any  displacement  at  all  can  be 
seen  even  among  the  nearest  stars.  The  parallaxes 
of  perhaps  a  hundred  stars  have  been  determined, 
with  greater  or  less  precision,  and  a  few  hundred  more 
may  be  near  enough  for  measurement.  All  the  others 
are  immeasurably  distant ;  and  it  is  only  by  statistical 
methods  based  on  their  proper  motions  and  their 
probable  near  approach  to  equality  in  distribution 
that  any  idea  can  be  gained  of  their  distances. 

To  form  a  conception  of  the  stellar  system,  we  must 
have  a  unit  of  measure  not  only  exceeding  any  ter- 
restrial standard,  but  even  any  distance  in  the  solar 
system.  For  purely  astronomical  purposes  the  most 
convenient  unit  is  the  distance  corresponding  to  a 
parallax  of  i",  which  is  a  little  more  than  200,000 
times  the  sun's  distance.  But  for  the  purposes  of 
all  but  the  professional  astronomer  the  most  conven- 

44 


A    TYPICAL    STAR    CLUSTER CENTAURI 


THE  STRUCTURE  OF  THE  UNIVERSE 

lent  unit  will  be  the  light-year — that  is,  the  distance 
.  through  which  light  would  travel  in  one  year.  This 
is  equal  to  the  product  of  186,000  miles,  the  distance 
travelled  in  one  second,  by  31,558,000,  the  number 
of  seconds  in  a  year.  The  reader  who  chooses  to  do 
so  may  perform  the  multiplication  for  himself.  The 
product  will  amount  to  about  63,000  times  the  dis- 
tance of  the  sun. 

The  nearest  star  whose  distance  we  know,  Alpha 
Centauri,  is  distant  from  us  more  than  four  light- 
years.  In  all  likelihood  this  is  really  the  nearest 
star,  and  it  is  not  at  all  probable  that  any  other 
star  lies  within  six  light-years.  Moreover,  if  we  were 
transported  to  this  star  the  probability  seems  to  be 
that  the  sun  would  now  be  the  nearest  star  to  us. 
Flying  to  any  other  of  the  stars  whose  parallax  has 
been  measured,  we  should  probably  find  that  the 
average  of  the  six  or  eight  nearest  stars  around  us 
ranges  somewhere  between  five  and  seven  light-years. 
We  may,  in  a  certain  sense,  call  eight  light-years  a 
star-distance,  meaning  by  this  term  the  average  of 
the  nearest  distances  from  one  star  to  th£  surround- 
ing ones. 

To  put  the  result  of  measures  of  parallax  into  an- 
other form,  let  us  suppose,  described  around  our  sun 
as  a  centre,  a  system  of  concentric  spheres  each  of 
whose  surfaces  is  at  the  distance  of  six  light-years 
outside  the  sphere  next  within  it.  The  inner  is  at 
the  distance  of  six  light-years  around  the  sun.  The 
surface  of  the  second  sphere  will  be  twelve  light-years 
away,  that  of  the  third  eighteen,  etc.  The  volumes 
of  space  within  each  of  these  spheres  will  be  as  the 
cubes  of.  the  diameters.  The  most  likely  conclusion 
we  can  draw  from  measures  of  parallax  is  that  the 

45 


SIDE-LIGHTS    ON    ASTRONOMY 

first  sphere  will  contain,  beside  the  sun  at  its  centre, 
only  Alpha  Centauri.  The  second,  twelve  light-years 
away,  will  probably  contain,  besides  these  two,  six 
other  stars,  making  eight  in  all.  The  third  may  con- 
tain twenty-one  more,  making  twenty-seven  stars 
within  the  third  sphere,  which  is  the  cube  of  three. 
Within  the  fourth  would  probably  be  found  sixty- 
four  stars,  this  being  the  cube  of  four,  and  so  on. 

Beyond  this  no  measures  of  parallax  yet  made  will 
give  us  much  assistance.  We  can  only  infer  that 
probably  the  same  law  holds  for  a  large  number  of 
spheres,  though  it  is  quite  certain  that  it  does  not 
hold  indefinitely.  For  more  light  on  the  subject  we 
must  have  recourse  to  the  proper  motions.  The  latest 
words  of  astronomy  on  this  subject  may  be  briefly 
summarized.  As  a  rule,  no  star  is  at  rest.  Each  is 
moving  through  space  with  a  speed  which  differs 
greatly  with  different  stars,  but  is  nearly  always  swift, 
indeed,  when  measured  by  any  standard  to  which  we 
are  accustomed.  Slow  and  halting,  indeed,  is  that 
star  which  does  not  make  more  than  a  mile  a  second. 
With  two  or  three  exceptions,  where  the  attraction 
of  a  companion  comes  in,  the  motion  of  every  star, 
so  far  as  yet  determined,  takes  place  in  a  straight 
line.  In  its  outward  motion  the  flying  body  deviates 
neither  to  the  right  nor  left.  It  is  safe  to  say  that, 
if  any  deviation  is  to  take  place,  thousands  of  years 
will  be  required  for  our  terrestrial  observers  to  recog- 
nize it. 

Rapid  as  the  course  of  these  objects  is,  the  dis- 
tances which  we  have  described  are  such  that,  in  the 
great  majority  of  cases,  all  the  observations  yet  made 
on  the  positions  of  the  stars  fail  to  show  any  well- 
established  motion.  It  is  only  in  the  case  of  the 

46 


THE  STRUCTURE  OF  THE  UNIVERSE 

nearer  of  these  objects  that  we  can  expect  any  mo- 
tion to  be  perceptible  during  the  period,  in  no  case 
exceeding  one  hundred  and  fifty  years,  through  which 
accurate  observations  extend.  The  efforts  of  all  the 
observatories  which  engage  in  such  work  are,  up  to 
the  present  time,  unequal  to  the  task  of  grappling 
with  the  motions  of  all  the  stars  that  can  be  seen 
with  the  instruments,  and  reaching  a  decision  as  to 
the  proper  motion  in  each  particular  case.  As  the 
question  now  stands,  the  aim  of  the  astronomer  is  to 
determine  what  stars  have  proper  motions  large 
enough  to  be  well  established.  To  make  our  state- 
ment on  this  subject  clear,  it  must  be  understood 
that  by  this  term  the  astronomer  does  not  mean  the 
speed  of  a  star  in  space,  but  its  angular  motion  as  he 
observes  it  on  the  celestial  sphere.  A  star  moving 
forward  with  a  given  speed  will  have  a  greater  proper 
motion  according  as  it  is  nearer  to  us.  To  avoid  all 
ambiguity,  we  shall  use  the  term  " speed"  to  express 
the  velocity  in  miles  per  second  with  which  such  a 
body  moves  through  space,  and  the  term  "  proper 
motion"  to  express  the  apparent  angular  motion 
which  the  astronomer  measures  upon  the  celestial 
sphere. 

Up  to  the  present  time,  two  stars  have  been  found 
whose  proper  motions  are  so  large  that,  if  continued, 
the  bodies  would  make  a  complete  circuit  of  the 
heavens  in  less  than  200,000  years.  One  of  these 
would  require  about  160,000;  the  other  about  180,- 
ooo  years  for  the  circuit.  Of  other  stars  having  a 
rapid  motion  only  about  one  hundred  would  com- 
plete their  course  in  less  than  a  million  of  years. 

Quite  recently  a  system  of  observations  upon  stars 
to  the  ninth  magnitude  has  been  nearly  carried 

47 


SIDE-LIGHTS    ON    ASTRONOMY 

through  by  an  international  combination  of  observa- 
tories. The  most  important  conclusion  from  these 
observations  relates  to  the  distribution  of  the  stars 
with  reference  to  the  Milky  Way,  which  we  have  al- 
ready described.  We  have  shown  that  stars  of  every 
magnitude,  bright  and  faint,  show  a  tendency  to 
crowd  towards  this  belt.  It  is,  therefore,  remark- 
able that  no  such  tendency  is  seen  in  the  case  of  those 
stars  which  have  proper  motions  large  enough  to  be 
accurately  determined.  So  far  as  yet  appears,  such 
stars  are  equally  scattered  over  the  heavens,  without 
reference  to  the  course  of  the  Milky  Way.  The  con- 
clusion is  obvious.  These  stars  are  all  inside  the 
girdle  of  the  Milky  Way,  and  within  the  sphere  which 
contains  them  the  distribution  in  space  is  approxi- 
mately uniform.  At  least  there  is  no  well-marked 
condensation  in  the  direction  of  the  galaxy  nor  any 
marked  thinning  out  towards  its  poles.  What  can 
we  say  as  to  the  extent  of  this  sphere  ? 

To  answer  this  question,  we  have  to  consider 
whether  there  is  any  average  or  ordinary  speed  that 
a  star  has  in  space.  A  great  number  of  motions  in 
the  line  of  sight — that  is  to  say,  in  the  direction  of 
the  line  from  us  to  the  star — have  been  measured 
with  great  precision  by  Campbell  at  the  Lick  Ob- 
servatory, and  by  other  astronomers.  The  statisti- 
cal investigations  of  Kaptoyn  also  throw  much  light 
on  the  subject.  The  results  of  these  investigators 
agree  well  in  showing  an  average  speed  in  space — a 
straight-ahead  motion  we  may  call  it — of  twenty-one 
miles  per  second.  Some  stars  may  move  more  slow- 
ly than  this  to  any  extent;  others  more  rapidly.  In 
two  or  three  cases  the  speed  exceeds  one  hundred 
miles  per  second,  but  these  are  quite  exceptional. 

48 


THE  STRUCTURE  OF  THE  UNIVERSE 

By  taking  several  thousand  stars  having  a  given 
proper  motion,  we  may  form  a  general  idea  of  their 
average  distance,  though  a  great  number  of  them 
will  exceed  this  average  to  a  considerable  extent. 
The  conclusion  drawn  in  this  way  would  be  that  the 
stars  having  an  apparent  proper  motion  of  10" 
per  century  or  more  are  mostly  contained  within,  or 
lie  not  far  outside  of  a  sphere  whose  surface  is  at  a 
distance  from  us  of  200  light-years.  Granting  the 
volume  of  space  which  we  have  shown  that  nature 
seems  to  allow  to  each  star,  this  sphere  should  con- 
tain 27,000  stars  in  all.  There  are  about  10,000 
stars  known  to  have  so  large  a  proper  motion  as  10". 
But  there  is  no  actual  discordance  between  these 
results,  because  not  only  are  there,  in  all  probability, 
great  numbers  of  stars  of  which  the  proper  motion 
is  not  yet  recognized,  but  there  are  within  the  sphere 
a  great  number  of  stars  whose  motion  is  less  than  the 
average.  On  the  other  hand,  it  is  probable  that  a 
considerable  number  of  the  10,000  stars  lie  at  a  dis- 
tance at  least  one-half  greater  than  that  of  the  radius 
of  the  sphere. 

On  the  whole,  it  seems  likely  that,  out  to  a  distance 
of  300  or  even  400  light-years,  there  is  no  marked 
inequality  in  star  distribution.  If  we  should  explore 
the  heavens  to  this  distance,  we  should  neither  find 
the  beginning  of  the  Milky  Way  in  one  direction  nor 
a  very  marked  thinning  out  in  the  other.  This 
conclusion  is  quite  accordant  with  the  probabili- 
ties of  the  case.  If  all  the  stars  which  form  the 
groundwork  of  the  Milky  Way  should  be  blotted 
out,  we  should  probably  find  100,000,000,  perhaps 
even  more,  remaining.  Assigning  to  each  star  the 
space  already  shown  to  be  its  quota,  we  should  re- 

49 


SIDE-LIGHTS    ON    ASTRONOMY 

quire  a  sphere  of  about  3000  light-years  radius  to 
contain  such  a  number  of  stars.  At  some  such  dis- 
tance as  this,  we  might  find  a  thinning  out  of  the 
stars  in  the  direction  of  the  galactic  poles,  or  the 
commencement  of  the  Milky  Way  in  the  direction  of 
this  stream. 

Even  if  this  were  not  found  at  the  distance  which 
we  have  supposed,  it  is  quite  certain  that,  at  some 
greater  distance,  we  should  at  least  find  that  the 
region  of  the  Milky  Way  is  richer  in  stars  than  the 
region  near  the  galactic  poles.  There  is  strong  rea- 
son, based  on  the  appearance  of  the  stars  of  the 
Milky  Way,  their  physical  constitution,  and  their 
magnitudes  as  seen  in  the  telescope,  to  believe  that, 
were  we  placed  on  one  of  these  stars,  we  should  find 
the  stars  around  us  to  be  more  thickly  strewn  than 
they  are  around  our  system.  In  other  words,  the 
quota  of  space  filled  by  each  star  is  probably  less  in 
the  region  of  the  Milky  Way  than  it  is  near  the  centre 
where  we  seem  to  be  situated. 

We  are,  therefore,  presented  with  what  seems  to 
be  the  most  extraordinary  spectacle  that  the  universe 
can  offer,  a  ring  of  stars  spanning  it,  and  including 
within  its  limits  by  far  the  great  majority  of  the 
stars  within  our  system.  We  have  in  this  spectacle 
another  example  of  the  unity  which  seems  to  per- 
vade the  system.  We  might  imagine  the  latter  so 
arranged  as  to  show  diversity  to  any  extent.  We 
might  have  agglomerations  of  stars  like  those  of  the 
Milky  Way  situated  in  some  corner  of  the  system, 
or  at  its  centre,  or  scattered  through  it  here  and  there 
in  every  direction.  But  such  is  not  the  case.  There 
are,  indeed,  a  few  star-clusters  scattered  here  and 
there  through  the  system;  but  they  are  essentially 

50 


THE  STRUCTURE  OF  THE  UNIVERSE 

different  from  the  clusters  of  the  Milky  Way,  and 
cannot  be  regarded  as  forming  an  important  part  of 
the  general  plan.  In  the  case  of  the  galaxy  we  have 
no  such  scattering,  but  find  the  stars  built,  as  it  were, 
into  this  enormous  ring,  having  similar  characteristics 
throughout  nearly  its  whole  extent,  and  having  within 
it  a  nearly  uniform  scattering  of  stars,  with  here  and 
there  some  collected  into  clusters.  Such,  to  our  limited 
vision,  now  appears  the  universe  as  a  whole. 

We  have  already  alluded  to  the  conclusion  that  an 
absolutely  infinite  system  of  stars  would  cause  the 
entire  heavens  to  be  filled  with  a  blaze  of  light  as 
bright  as  the  sun.  It  is  also  true  that  the  attractive 
force  within  such  a  universe  would  be  infinitely  great 
in  some  direction  or  another.  But  neither  of  these 
considerations  enables  us  to  set  a  limit  to  the  extent 
of  our  system.  In  two  remarkable  papers  by  Lord 
Kelvin  which  have  recently  appeared,  the  one  being 
an  address  before  the  British  Association  at  its  Glas- 
gow meeting,  in  1901,  are  given  the  results  of  some 
numerical  computations  pertaining  to  this  subject. 
Granting  that  the  stars  are  scattered  promiscuously 
through  space  with  some  approach  to  uniformity  in 
thickness,  and  are  of  a  known  degree  of  brilliancy, 
it  is  easy  to  compute  how  far  out  the  system  must 
extend  in  order  that,  looking  up  at  the  sky,  we  shall 
see  a  certain  amount  of  light  coming  from  the  in- 
visible stars.  Granting  that,  in  the  general  average, 
each  star  is  as  bright  as  the  sun,  and  that  their  thick- 
ness is  such  that  within  a  sphere  of  3300  light-years 
there  are  1,000,000,000  stars,  if  we  inquire  how  far 
out  such  a  system  must  be  continued  in  order  that 
the  sky  shall  shine  with  even  four  per  cent,  of  the 
light  of  the  sun,  we  shall  find  the  distance  of  its  boun- 


SIDE-LIGHTS    ON    ASTRONOMY 

dary  so  great  that  millions  of  millions  of  years  would 
be  required  for  the  light  of  the  outer  stars  to  reach 
the  centre  of  the  system.  In  view  of  the  fact  that 
this  duration  in  time  far  exceeds  what  seems  to  be 
the  possible  life  duration  of  a  star,  so  far  as  our 
knowledge  of  it  can  extend,  the  mere  fact  that  the 
sky  does  not  glow  with  any  such  brightness  proves 
little  or  nothing  as  to  the  extent  of  the  system. 

We  may,  however,  replace  these  purely  negative 
considerations  by  inquiring  how  much  light  we  act- 
ually get  from  the  invisible  stars  of  our  system. 
Here  we  can  make  a  definite  statement.  Mark  out 
a  small  circle  in  the  sky  i°  in  diameter.  The  quan- 
tity of  light  which  we  receive  on  a  cloudless  and 
moonless  night  from  the  sky  within  this  circle  ad- 
mits of  actual  determination.  From  the  measures 
so  far  available  it  would  seem  that,  in  the  general 
average,  this  quantity  of  light  is  not  very  different 
from  that  of  a  star  of  the  fifth  magnitude.  This  is 
something  very  different  from  a  blaze  of  light.  A 
star  of  the  fifth  magnitude  is  scarcely  more  than 
plainly  visible  to  ordinary  vision.  The  area  of  the 
whole  sky  is,  in  round  numbers,  about  50,000  times 
that  of  the  circle  we  have  described.  It  follows  that 
the  total  quantity  of  light  which  we  receive  from  all 
the  stars  is  about  equal  to  that  of  50,000  stars  of  the 
fifth  magnitude — somewhat  more  than  1000  of  the 
first  magnitude.  This  whole  amount  of  light  would 
have  to  be  multiplied  by  90,000,000  to  make  a  light 
equal  to  that  of  the  sun.  It  is,  therefore,  not  at  all 
necessary  to  consider  how  far  the  system  must  ex- 
tend in  order  that  the  heavens  should  blaze  like  the 
sun.  Adopting  Lord  Kelvin's  hypothesis,  we  shall 
find  that,  in  order  that  we  may  receive  from  the  stars 

52 


THE  STRUCTURE  OF  THE  UNIVERSE 

the  amount  of  light  we  have  designated,  this  system 
need  not  extend  beyond  some  5000  light-years.  But 
this  hypothesis  probably  overestimates  the  thickness 
of  the  stars  in  space.  It  does  not  seem  probable  that 
there  are  as  many  as  1,000,000,000  stars  within  the 
sphere  of  3300  light-years.  Nor  is  it  at  all  certain 
that  the  light  of  the  average  star  is  equal  to  that  of 
the  sun.  It  is  impossible,  in  the  present  state  of  our 
knowledge,  to  assign  any  definite  value  to  this  aver- 
age. To  do  so  is  a  problem  similar  to  that  of  as- 
signing an  average  weight  to  each  component  of  the 
animal  creation,  from  the  microscopic  insects  which 
destroy  our  plants  up  to  the  elephant.  What  we  can 
say  with  a  fair  approximation  to  confidence  is  that, 
if  we  could  fly  out  in  any  direction  to  a  distance  of 
20,000,  perhaps  even  of  10,000,  light-years,  we  should 
find  that  we  had  left  a  large  fraction  of  our  system 
behind  us.  We  should  see  its  boundary  in  the  direc- 
tion in  which  we  had  travelled  much  more  certainly 
than  we  see  it  from  our  stand-point. 

We  should  not  dismiss  this  branch  of  the  subject 
without  saying  that  considerations  are  frequently 
adduced  by  eminent  authorities  which  tend  to  im- 
pair our  confidence  in  almost  any  conclusion  as  to 
the  limits  of  the  stellar  system.  The  main  argument 
is  based  on  the  possibility  that  light  is  extinguished 
in  its  passage  through  space;  that  beyond  a  certain 
distance  we  cannot  see  a  star,  however  bright,  be- 
cause its  light  is  entirely  lost  before  reaching  us. 
That  there  could  be  any  loss  of  light  in  passing 
through  an  absolute  vacuum  of  any  extent  cannot 
be  admitted  by  the  physicist  of  to-day  without  im- 
pairing what  he  considers  the  fundamental  principles 
of  the  vibration  of  light.  But  the  possibility  that  the 

53 


SIDE-LIGHTS    ON    ASTRONOMY 

celestial  spaces  are  pervaded  by  matter  which  might 
obstruct  the  passage  of  light  is  to  be  considered. 
We  know  that  minute  meteoric  particles  are  flying 
through  our  system  in  such  numbers  that  the  earth 
encounters  several  millions  of  them  every  day,  which 
appear  to  us  in  the  familiar  phenomena  of  shooting- 
stars.  If  such  particles  are  scattered  through  all 
space,  they  must  ultimately  obstruct  the  passage  of 
light.  We  know  little  of  the  size  of  these  bodies,  but, 
from  the  amount  of  energy  contained  in  their  light 
as  they  are  consumed  in  the  passage  through  our 
atmosphere,  it  does  not  seem  at  all  likely  that  they 
are  larger  than  grains  of  sand  or,  perhaps,  minute 
pebbles.  They  are  probably  vastly  more  numerous 
in  the  vicinity  of  the  sun  than  in  the  interstellar 
spaces,  since  they  would  naturally  tend  to  be  collected 
by  the  sun's  attraction.  In  fact  there  are  some  rea- 
sons for  believing  that  most  of  these  bodies  are  the 
debris  of  comets;  and  the  latter  are  now  known  to 
belong  to  the  solar  system,  and  not  to  the  universe 
at  large. 

But  whatever  view  we  take  of  these  possibilities, 
they  cannot  invalidate  our  conclusion  as  to  the  gen- 
eral structure  of  the  stellar  system  as  we  know  it. 
Were  meteors  so  numerous  as  to  cut  off  a  large  frac- 
tion of  the  light  from  the  more  distant  stars,  we 
should  see  no  Milky  Way,  but  the  apparent  thick- 
ness of  the  stars  in  every  direction  would  be  nearly 
the  same.  The  fact  that  so  many  more  of  these 
objects  are  seen  around  the  galactic  belt  than  in  the 
direction  of  its  poles  shows  that,  whatever  extinction 
light  may  suffer  in  going  through  the  greatest  dis- 
tances, we  see  nearly  all  that  comes  from  stars  not 
more  distant  than  the  Milky  Way  itself. 

54 


THE  STRUCTURE  OF  THE  UNIVERSE 

Intimately  connected  with  the  subject  we  have 
discussed  is  the  question  of  the  age  of  our  system,  if 
age  it  can  be  said  to  have.  In  considering  this  ques- 
tion, the  simplest  hypothesis  to  suggest  itself  is  that 
the  universe  has  existed  forever  in  some  such  form 
as  we  now  see  it;  that  it  is  a  self-sustaining  system, 
able  to  go  on  forever  with  only  such  cycles  of  trans- 
formation as  may  repeat  themselves  indefinitely,  and 
may,  therefore,  have  repeated  themselves  indefinitely 
in  the  past.  Ordinary  observation  does  not  make 
anything  known  to  us  which  would  seem  to  invali- 
date this  hypothesis.  In  looking  upon  the  opera- 
tions of  the  universe,  we  may  liken  ourselves  to  a 
visitor  to  the  earth  from  another  sphere  who  has  to 
draw  conclusions  about  the  life  of  an  individual  man 
from  observations  extending  through  a  few  days. 
During  that  time,  he  would  see  no  reason  why  the 
life  of  the  man  should  have  either  a  beginning  or  an 
end.  He  sees  a  daily  round  of  change,  activity  and 
rest,  nutrition  and  waste ;  but,  at  the  end  of  the  round, 
the  individual  is  seemingly  restored  to  his  state  of 
the  day  before.  Why  may  not  this  round  have  been 
going  on  forever,  and  continue  in  the  future  without 
end  ?  It  would  take  a  profounder  course  of  observa- 
tion and  a  longer  time  to  show  that,  notwithstanding 
this  seeming  restoration,  an  imperceptible  residual 
of  vital  energy,  necessary  to  the  continuance  of  life, 
has  not  been  restored,  and  that  the  loss  of  this  re- 
siduum day  by  day  must  finally  result  in  death. 

The  case  is  much  the  same  with  the  great  bodies 
of  the  universe.  Although,  to  superficial  observa- 
tion, it  might  seem  that  they  could  radiate  their  light 
forever,  the  modern  generalizations  of  physics  show 
that  such  cannot  be  the  case.  The  radiation  of  light 
s  55 


SIDE-LIGHTS    ON    ASTRONOMY 

necessarily  involves  a  corresponding  loss  of  heat  and 
with  it  the  expenditure  of  some  form  of  energy. 
The  amount  of  energy  within  any  body  is  necessarily 
limited.  The  supply  must  be  exhausted  unless  the 
energy  of  the  light  sent  out  into  infinite  space  is,  in 
some  way,  restored  to  the  body  which  expended  it. 
The  possibility  of  such  a  restoration  completely  tran- 
scends our  science.  How  can  the  little  vibration 
which  strikes  our  eye  from  some  distant  star,  and 
which  has  been  perhaps  thousands  of  years  in  reach- 
ing us,  find  its  way  back  to  its  origin?  The  light 
emitted  by  the  sun  10,000  years  ago  is  to-day  pur- 
suing its  way  in  a  sphere  whose  surface  is  10,000 
light-years  distant  on  all  sides.  Science  has  nothing 
even  to  suggest  the  possibility  of  its  restoration,  and 
the  most  delicate  observations  fail  to  show  any  re- 
turn from  the  unfathomable  abyss. 

Up  to  the  time  when  radium  was  discovered,  the 
most  careful  investigations  of  .all  conceivable  sources 
of  supply  had  shown  only  one  which  could  possibly 
be  of  long  duration.  This  is  the  contraction  which  is 
produced  in  the  great  incandescent  bodies  of  the  uni- 
verse by  the  loss  of  the  heat  which  they  radiate.  As 
remarked  in  the  preceding  essay,  the  energy  gene- 
rated by  the  sun's  contraction  could  not  have  kept 
up  its  present  supply  of  heat  for  much  more  than 
twenty  or  thirty  millions  of  years,  while  the  study 
of  earth  and  ocean  shows  evidence  of  the  action  of  a 
series  of  causes  which  must  have  been  going  on  for 
hundreds  of  millions  of  years. 

The  antagonism  between  the  two  conclusions  is 
even  more  marked  than  would  appear  from  this 
statement.  The  period  of  the  sun's  heat  set  by  the 
astronomical  physicist  is  that  during  which  our 

56 


THE  STRUCTURE  OF  THE  UNIVERSE 

luminary  could  possibly  have  existed  in  its  present 
form.  The  period  set  by  the  geologist  is  not  merely 
that  of  the  sun's  existence,  but  that  during  which 
the  causes  effecting  geological  changes  have  not 
undergone  any  complete  revolution.  If,  at  any  time, 
the  sun  radiated  much  less  than  its  present  amount 
of  heat,  no  water  could  have  existed  on  the  earth's 
surface  except  in  the  form  of  ice;  there  would  have 
been  scarcely  any  evaporation,  and  the  geological 
changes  due  to  erosion  could  not  have  taken  place. 
Moreover,  the  commencement  of  the  geological  opera- 
tions of  which  we  speak  is  by  no  means  the  commence- 
ment of  the  earth's  existence.  The  theories  of  both 
parties  agree  that,  for  untold  aeons  before  the  geo- 
logical changes  now  visible  commenced,  our  planet 
was  a  molten  mass,  perhaps  even  an  incandescent 
globe  like  the  sun.  During  all  those  aeons  the  sun 
must  have  been  in  existence  as  a  vast  nebulous  mass, 
first  reaching  as  far  as  the  earth's  orbit,  and  slowly 
contracting  its  dimensions.  And  these  aeons  are  to 
be  included  in  any  estimate  of  the  age  of  the  sun. 

The  doctrine  of  cosmic  evolution — the  theory  which 
in  former  times  was  generally  known  as  the  nebular 
hypothesis — that  the  heavenly  bodies  were  formed 
by  the  slow  contraction  of  heated  nebulous  masses, 
is  indicated  by  so  many  facts  that  it  seems  scarcely 
possible  to  doubt  it  except  on  the  theory  that  the 
laws  of  nature  were,  at  some  former  time,  different 
from  those  which  we  now  see  in  operation.  Grant- 
ing the  evolutionary  hypothesis,  every  star  has  its 
lifetime.  We  can  even  lay  down  the  law  by  which 
it  passes  from  infancy  to  old  age.  All  stars  do  not 
have  the  same  length  of  life ;  the  rule  is  that  the  larger 
the  star,  or  the  greater  the  mass  of  matter  which 

57 


SIDE-LIGHTS    ON    ASTRONOMY 

composes  it,  the  longer  will  it  endure.  Up  to  the 
present  time,  science  can  do  nothing  more  than  point 
out  these  indications  of  a  beginning,  and  their  in- 
evitable consequence,  that  there  is  to  be  an  end  to 
the  light  and  heat  of  every  heavenly  body.  But  no 
cautious  thinker  can  treat  such  a  subject  with  the 
ease  of  ordinary  demonstration.  The  investigator 
may  even  be  excused  if  he  stands  dumb  with  awe  be- 
fore the  creation  of  his  own  intellect.  Our  accurate 
records  of  the  operations  of  nature  extend  through 
only  two  or  three  centuries,  and  do  not  reach  a  satis- 
factory standard  until  within  a  single  century.  The 
experience  of  the  individual  is  limited  to  a  few  years, 
and  beyond  this  period  he  must  depend  upon  the 
records  of  his  ancestors.  All  his  knowledge  of  the 
laws  of  nature  is  derived  from  this  very  limited  ex- 
perience. How  can  he  essay  to  describe  what  may 
have  been  going  on  hundreds  of  millions  of  years  in 
the  past?  Can  he  dare  to  say  that  nature  was  the 
same  then  as  now? 

It  is  a  fundamental  principle  of  •  the  theory  of 
evolution,  as  developed  by  its  greatest  recent  ex- 
pounder, that  matter  itself  is  eternal,  and  that  all 
the  changes  which  have  taken  place  in  the  universe, 
so  far  as  made  up  of  matter,  are  in  the  nature  of  trans- 
formations of  this  eternal  substance.  But  we  doubt 
whether  any  physical  philosopher  of  the  present  day 
would  be  satisfied  to  accept  any  demonstration  of 
the  eternity  of  matter.  All  he  would  admit  is  that, 
so  far  as  his  observation  goes,  no  change  in  the  quan- 
tity of  matter  can  be  produced  by  the  action  of 
any  known  cause.  It  seems  to  be  equally  uncrea table 
and  indestructible.  But  he  would,  at  the  same  time, 
admit  that  his  experience  no  more  sufficed  to  settle 

S8 


THE  STRUCTURE  OF  THE  UNIVERSE 

the  question  than  the  observation  of  an  animal  for 
a  single  day  would  settle  the  question  of  the  duration 
of  its  life,  or  prove  that  it  had  neither  beginning  nor 
end.  He  would  probably  admit  that  even  matter 
itself  may  be  a  product  of  evolution.  The  astronomer 
finds  it  difficult  to  conceive  that  the  great  nebulous 
masses  which  he  sees  in  the  celestial  spaces — millions 
of  times  larger  than  the  whole  solar  system,  yet  so 
tenuous  that  they  offer  not  the  slightest  obstruction 
to  the  passage  of  a  ray  of  light  through  their  whole 
length — situated  in  what  seems  to  be  a  region  of 
eternal  cold,  below  anything  that  we  can  produce  on 
the  earth's  surface,  yet  radiating  light,  and  with  it 
heat,  like  an  incandescent  body — can  be  made  up  of 
the  same  kind  of  substance  that  we  have  around  us 
on  the  earth's  surface.  Who  knows  but  that  the 
radiant  property  that  Becquerel  has  found  in  certain 
forms  of  matter  may  be  a  residuum  of  some  original 
form  of  energy  which  is  inherent  in  great  cosmical 
masses,  and  has  fed  our  sun  during  all  the  ages  re- 
quired by  the  geologist  for  the  structure  of  the  earth's 
crusts  ?  It  may  be  that  in  this  phenomenon  we  have 
the  key  to  the  great  riddle  of  the  universe,  with  which 
profounder  secrets  of  matter  than  any  we  have  pene- 
trated will  be  opened  to  the  eyes  of  our  successors. 


IV 

THE    EXTENT   OF    THE    UNIVERSE 

WE  cannot  expect  that  the  wisest  men  of  our  re- 
motest posterity,  who  can  base  their  conclusions 
upon  thousands  of  years  of  accurate  observation,  will 
reach  a  decision  on  this  subject  without  some  meas- 
ure of  reserve.  Such  being  the  case,  it  might  appear 
the  dictate  of  wisdom  to  leave  its  consideration  to 
some  future  age,  when  it  may  be  taken  up  with  bet- 
ter means  of  information  than  we  now  possess.  But 
the  question  is  one  which  will  refuse  to  be  postponed 
so  long  as  the  propensity  to  think  of  the  possibilities 
of  creation  is  characteristic  of  our  race.  The  issue 
is  not  whether  we  shall  ignore  the  question  altogether, 
like  Eve  in  the  presence  of  Raphael;  but  whether 
in  studying  it  we  shall  confine  our  speculations  with- 
in the  limits  set  by  sound  scientific  reasoning.  Essay- 
ing to  do  this,  I  invite  the  reader's  attention  to  what 
science  may  suggest,  admitting  in  advance  that  the 
sphere  of  exact  knowledge  is  small  compared  with 
the  possibilities  of  creation,  and  that  outside  this 
sphere  we  can  state  only  more  or  less  probable  con- 
clusions. 

The  "reader  who  desires  to  approach  this  subject  in 
the  most  receptive  spirit  should  begin  his  study  by 
betaking  himself  on  a  clear,  moonless  evening,  when 
he  has  no  earthly  concern  to  disturb  the  serenity  of 

60 


THE  EXTENT  OF  THE  UNIVERSE 

his  thoughts,  to  some  point  where  he  can  lie  on  his 
back  on  bench  or  roof,  and  scan  the  whole  vault  of 
heaven  at  one  view.  He  can  do  this  with  the  great- 
est pleasure  and  profit  in  late  summer  or  autumn- 
winter  would  do  equally  well  were  it  possible  for  the 
mind  to  rise  so  far  above  bodily  conditions  that  the 
question  of  temperature  should  not  enter.  The  think- 
ing man  who  does  this  under  circumstances  most  favor- 
able for  calm  thought  will  form  a  new  conception  of 
the  wonder  of  the  universe.  If  summer  or  autumn  be 
chosen,  the  stupendous  arch  of  the  Milky  Way  will 
pass  near  the  zenith,  and  the  constellation  Lyra,  led 
by  its  beautiful  blue  Vega  of  the  first  magnitude,  may 
be  not  very  far  from  that  point.  South  of  it  will  be 
seen  the  constellation  Aquila,  marked  by  the  bright 
Altair,  between  two  smaller  but  conspicuous  stars. 
The  bright  Arcturus  will  be  somewhere  in  the  west, 
and,  if  the  observation  is  not  made  too  early  in  the 
season,  Aldebaran  will  be  seen  somewhere  in  the  east. 
When  attention  is  concentrated  on  the  scene  the 
thousands  of  stars  on  each  side  of  the  Milky  Way 
will  fill  the  mind  with  the  consciousness  of  a  stupen- 
dous and  all-embracing  frame,  beside  which  all  human 
affairs  sink  into  insignificance.  A  new  idea  will  be 
formed  of  such  a  well-known  fact  of  astronomy  as 
the  motion  of  the  solar  system  in  space,  by  reflecting 
that,  during  all  human  history,  the  sun,  carrying  the 
earth  with  it,  has  been  flying  towards  a  region  in  or 
just  south  of  the  constellation  Lyra,  with  a  speed  be- 
yond all  that  art  can  produce  on  earth,  without  pro- 
ducing any  change  apparent  to  ordinary  vision  in 
the  aspect  of  the  constellation.  Not  only  Lyra  and 
Aquila,  but  every  one  of  the  thousand  stars  which 
form  the  framework  of  the  sky,  were  seen  by  our 

61 


SIDE-LIGHTS    ON    ASTRONOMY 

earliest  ancestors  just  as  we  see  them  now.  Bodily 
rest  may  be  obtained  at  any  time  by  ceasing  from 
our  labors,  and  weary  systems  may  find  nerve  rest 
at  any  summer  resort;  but  I  know  of  no  way  in 
which  complete  rest  can  be  obtained  for  the  weary 
soul — in  which  the  mind  can  be  so  entirely  relieved 
of  the  burden  of  all  human  anxiety — as  by  the  con- 
templation of  the  spectacle  presented  by  the  starry 
heavens  under  the  conditions  just  described.  As  we 
make  a  feeble  attempt  to  learn  what  science  can  tell 
us  about  the  structure  of  this  starry  frame,  I  hope 
the  reader  will  allow  me  to  at  least  fancy  him  con- 
templating it  in  this  way. 

The  first  question  which  may  suggest  itself  to  the 
inquiring  reader  is:  How  is  it  possible  by  any  methods 
of  observation  yet  known  to  the  astronomer  to  learn 
anything  about  the  universe  as  a  whole?  We  may 
commence  by  answering  this  question  in  a  somewhat 
comprehensive  way.  It  is  possible  only  because  the 
universe,  vast  though  it  is,  shows  certain  character- 
istics of  a  unified  and  bounded  whole.  It  is  not  a 
chaos,  it  is  not  even  a  collection  of  things,  each  of 
which  came  into  existence  in  its  own  separate  way. 
If  it  were,  there  would  be  nothing  in  common  between 
two  widely  separate  regions  of  the  universe.  But, 
as  a  matter  of  fact,  science  shows  unity  in  the  whole 
structure,  and  diversity  only  in  details.  The  Milky 
Way  itself  will  be  seen  by  the  most  ordinary  ob- 
server to  form  a  single  structure.  This  structure  is, 
in  some  sort,  the  foundation  on  which  the  universe  is 
built.  It  is  a  girdle  which  seems  to  span  the  whole 
of  creation,  so  far  as  our  telescopes  have  yet  enabled 
us  to  determine  what  creation  is ;  and  yet  it  has  ele- 
ments of  similarity  in  all  its  parts.  What  has  yet 

62 


THE  EXTENT  OF  THE  UNIVERSE 

more  significance,  it  is  in  some  respects  unlike  those 
parts  of  the  universe  which  lie  without  it,  and  even 
unlike  those  which  lie  in  that  central  region  within 
it  where  our  system  is  now  situated.  The  minute 
stars,  individually  far  beyond  the  limit  of  visibility 
to  the  naked  eye,  which  form  its  cloudlike  agglomera- 
tions, are  found  to  be  mostly  bluer  in  color,  from  one 
extreme  to  the  other,  than  the  general  average  of 
the  stars  which  make  up  the  rest  of  the  universe. 

In  the  preceding  essay  on  the  structure  of  the  uni- 
verse, we  have  pointed  out  several  features  of  the 
universe  showing  the  unity  of  the  whole.  We  shall 
now  bring  together  these  and  other  features  with  a 
view  of  showing  their  relation  to  the  question  of  the 
extent  of  the  universe. 

The  Milky  Way  being  in  a  certain  sense  the  founda- 
tion on  which  the  whole  system  is  constructed,  we 
have  first  to  notice  the  symmetry  of  the  whole.  This 
is  seen  in  the  fact  that  a  certain  resemblance  is  found 
in  any  two  opposite  regions  of  the  sky,  no  matter 
where  we  choose  them.  If  we  take  them  in  the 
Milky  Way,  the  stars  are  more  numerous  than  else- 
where; if  we  take  opposite  regions  in  or  near  the 
Milky  Way,  we  shall  find  more  stars  in  both  of  them 
than  elsewhere;  if  we  take  them  in  the  region  any- 
where around  the  poles  of  the  Milky  Way,  we  shall 
find  fewer  stars,  but  they  will  be  equally  numerous 
in  each  of  the  two  regions.  We  infer  from  this  that 
whatever  cause  determined  the  number  of  the  stars 
in  space  was  of  the  same  nature  in  every  two  antip- 
odal regions  of  the  heavens. 

Another  unity  marked  with  yet  more  precision  is 
seen  in  the  chemical  elements  of  which  stars  are 
composed.  We  know  that  the  sun  is  composed  of 

63 


SIDE-LIGHTS    ON    ASTRONOMY 

the  same  elements  which  we  find  on  the  earth  and 
into  which  we  resolve  compounds  in  our  laboratories. 
These  same  elements  are  found  in  the  most  distant 
stars.  It  is  true  that  some  of  these  bodies  seem  to 
contain  elements  which  we  do  not  find  on  earth. 
But  as  these  unknown  elements  are  scattered  from 
one  extreme  of  the  universe  to  the  other,  they  only 
serve  still  further  to  enforce  the  unity  which  runs 
through  the  whole.  The  nebulae  are  composed,  in 
part  at  least,  of  forms  of  matter  dissimilar  to  any 
with  which  we  are  acquainted.  But,  different  though 
they  may  be,  they  are  alike  in  their  general  character 
throughout  the  whole  field  we  are  considering.  Even 
in  such  a  feature  as  the  proper  motions  of  the  stars, 
the  same  unity  is  seen.  The  reader  doubtless  knows 
that  each  of  these  objects  is  flying  through  space  on 
its  own  course  with  a  speed  comparable  with  that  of 
the  earth  around  the  sun.  These  speeds  range  from 
the  smallest  limit  up  to  more  than  one  hundred  miles 
a  second.  Such  diversity  might  seem  to  detract 
from  the  unity  of  the  whole;  but  when  we  seek  to 
learn  something  definite  by  taking  their  average,  we 
find  this  average  to  be,  so  far  as  can  yet  be  deter- 
mined, much  the  same  in  opposite  regions  of  the 
universe.  Quite  recently  it  has  become  probable 
that  a  certain  class  of  very  bright  stars  known  as 
Orion  stars — because  there  are  many  of  them  in  the 
most  brilliant  of  our  constellations — which  are  scat- 
tered along  the  whole  course  of  the  Milky  Way,  have 
one  and  all,  in  the  general  average,  slower  motions 
than  other  stars.  Here  again  we  have  a  definable 
characteristic  extending  through  the  universe.  In 
drawing  attention  to  these  points  of  similarity 
throughout  the  whole  universe,  it  must  not  be  sup- 

64 


THE    EXTENT    OF    THE    UNIVERSE 

posed  that  we  base  our  conclusions  directly  upon 
them.  The  point  they  bring  out  is  that  the  universe 
is  in  the  nature  of  an  organized  system ;  and  it  is  upon 
the  fact  of  its  being  such  a  system  that  we  are  able, 
by  other  facts,  to  reach  conclusions  as  to  its  struct- 
ure, extent,  and  other  characteristics. 

One  of  the  great  problems  connected  with  the  uni- 
verse is  that  of  its  possible  extent.  How  far  away 
are  the  stars  ?  One  of  the  unities  which  we  have  de- 
scribed leads  at  once  to  the  conclusion  that  the  stars 
must  be  at  very  different  distances  from  us ;  probably 
the  more  distant  ones  are  a  thousand  times  as  far  as 
the  nearest;  possibly  even  farther  than  this.  This 
conclusion  may,  in  the  first  place,  be  based  on  the 
fact  that  the  stars  seem  to  be  scattered  equally 
throughout  those  regions  of  the  universe  which  are 
not  connected  with  the  Milky  Way.  To  illustrate 
the  principle,  suppose  a  farmer  to  sow  a  wheat-field 
of  entirely  unknown  extent  with  ten  bushels  of  wheat. 
We  visit  the  field  and  wish  to  have  some  idea  of  its 
acreage.  We  may  do  this  if  we  know  how  many 
grains  of  wheat  there  are  in  the  ten  bushels.  Then  we 
examine  a  space  two  or  three  feet  square  in  any  part 
of  the  field  and  count  the  number  of  grains  in  that 
space.  If  the  wheat  is  equally  scattered  over  the 
whole  field,  we  find  its  extent  by  the  simple  rule 
that  the  size  of  the  field  bears  the  same  proportion 
to  the  size  of  the  space  in  which  the  count  was  made 
that  the  whole  number  of  grains  in  the  ten  bushels 
sown  bears  to  the  number  of  grains  counted.  If  we 
find  ten  grains  in  a  square  foot,  we  know  that  the 
number  of  square  feet  in  the  whole  field  is  one-tenth 
that  of  the  number  of  grains  sown.  So  it  is  with  the 
universe  of  stars.  If  the  latter  are  sown  equally 

65 


SIDE-LIGHTS    ON    ASTRONOMY 

through  space,  the  extent  of  the  space  occupied  must 
be  proportional  to  the  number  of  stars  which  it  con- 
tains. 

But  this  consideration  does  not  tell  us  anything 
about  the  actual  distance  of  the  stars  or  how  thickly 
they  may  be  scattered.  To  do  this  we  must  be  able 
to  determine  the  distance  of  a  certain  number  of 
stars,  just  as  we  suppose  the  farmer  to  count  the 
grains  in  a  certain  small  extent  of  his  wheat-field. 
There  is  only  one  way  in  which  we  can  make  a  defi- 
nite measure  of  the  distance  of  any  one  star.  As 
the  earth  swings  through  its  vast  annual  circuit 
round  the  sun,  the  direction  of  the  stars  must  ap- 
pear to  be  a  little  different  when  seen  from  one  ex- 
tremity of  the  circuit  than  when  seen  from  the  other. 
This  difference  is  called  the  parallax  of  the  stars ;  and 
the  problem  of  measuring  it  is  one  of  the  most  deli- 
cate and  difficult  in  the  whole  field  of  practical  as- 
tronomy. 

The  nineteenth  century  was  well  on  its  way  before 
the  instruments  of  the  astronomer  were  brought  to 
such  perfection  as  to  admit  of  the  measurement. 
From  the  time  of  Copernicus  to  that  of  Bessel  many 
attempts  had  been  made  to  measure  the  parallax  of 
the  stars,  and  more  than  once  had  some  eager  astron- 
omer thought  himself  successful.  But  subsequent 
investigation  always  showed  that  he  had  been  mis- 
taken, and  that  what  he  thought  was  the  effect  of 
parallax  was  due  to  some  other  cause,  perhaps  the 
imperfections  of  his  instrument,  perhaps  the  effect 
of  heat  and  cold  upon  it  or  upon  the  atmosphere 
through  which  he  was  obliged  to  observe  the  star, 
or  upon  the  going  of  his  clock.  Thus  things  went  on 
until  1837,  when  Bessel  announced  that  measures 

66 


THE    EXTE.NT    OF    THE    UNIVERSE 

with  a  heliometer — the  most  refined  instrument  that 
has  ever  been  used  in  measurement — showed  that  a 
certain  star  in  the  constellation  Cygnus  had  a  paral- 
lax of  one-third  of  a  second.  It  may  be  interesting 
to  give  an  idea  of  this  quantity.  Suppose  one's  self  in 
a  house  on  top  of  a  mountain  looking  out  of  a  window 
one  foot  square,  at  a  house  on  another  mountain  one 
hundred  miles  away.  One  is  allowed  to  look  at  that 
distant  house  through  one  edge  of  the  pane  of  glass 
and  then  through  the  opposite  edge ;  and  he  has  to 
determine  the  change  in  the  direction  of  the  distant 
house  produced  by  this  change  of  one  foot  in  his  own 
position.  From  this  he  is  to  estimate  how  far  off 
the  other  mountain  is.  To  do  this,  one  would  have 
to  measure  just  about  the  amount  of  parallax  that 
Bessel  found  in  his  star.  And  yet  this  star  is  among 
the  few  nearest  to  our  system.  The  nearest  star  of 
all,  Alpha  Centauri,  visible  only  in  latitudes  south  of 
our  middle  ones,  is  perhaps  half  as  far  as  Bessel's 
star,  while  Sirius  and  one  or  two  others  are  nearly 
at  the  same  distance.  About  100  stars,  all  told, 
have  had  their  parallax  measured  with  a  greater 
or  less  degree  of  probability.  The  work  is  going 
on  from  year  to  year,  each  successive  astronomer 
who  takes  it  up  being  able,  as  a  general  rule,  to  avail 
himself  of  better  instruments  or  to  use  a  better 
method.  But,  after  all,  the  distances  of  even  some 
of  the  100  stars  carefully  measured  must  still  remain 
quite  doubtful. 

Let  us  now  return  to  the  idea  of  dividing  the  space 
in  which  the  universe  is  situated  into  concentric 
spheres  drawn  at  various  distances  around  our  sys- 
tem as  a  centre.  Here  we  shall  take  as  our  stand- 
ard a  distance  400,000  times  that  of  the  sun  from 

67 


SIDE-LIGHTS    ON    ASTRONOMY 

the  earth.  Regarding  this  as  a  unit,  we  imagine 
ourselves  to  measure  out  in  any  direction  a  distance 
twice  as  great  as  this — then  another  equal  distance, 
making  one  three  times  as  great,  and  so  indefinitely. 
We  then  have  successive  spheres  of  which  we  take 
the  nearer  one  as  the  unit.  The  total  space  filled 
by  the  second  sphere  will  be  8  times  the  unit;  that 
of  the  third  space  27  times,  and  so  on,  as  the  cube 
of  each  distance.  Since  each  sphere  includes  all 
those  within  it,  the  volume  of  space  between  each 
two  spheres  will  be  proportional  to  the  difference  of 
these  numbers — that  is,  to  i,  7,  19,  etc.  Comparing 
these  volumes  with  the  number  of  stars  probably 
within  them,  the  general  result  up  to  the  present 
time  is  that  the  number  of  stars  in  any  of  these 
spheres  will  be  about  equal  to  the  units  of  volume 
which  they  comprise,  when  we  take  for  this  unit  the 
smallest  and  innermost  of  the  spheres,  having  a 
radius  400,000  times  the  sun's  distance.  We  are 
thus  enabled  to  form  some  general  idea  of  how  thick- 
ly the  stars  are  sown  through  space.  We  cannot 
claim  any  numerical  exactness  for  this  idea,  but  in 
the  absence  of  better  methods  it  does  afford  us  some 
basis  for  reasoning. 

Now  we  can  carry  on  our  computation  as  we  sup- 
posed the  farmer  to  measure  the  extent  of  his  wheat- 
field.  Let  us  suppose  that  there  are  125,000,000 
stars  in  the  heavens.  This  is  an  exceedingly  rough 
estimate,  but  let  us  make  the  supposition  for  the 
time  being.  Accepting  the  view  that  they  are  nearly 
equally  scattered  throughout  space,  it  will  follow 
that  they  must  be  contained  within  a  volume  equal 
to  125,000,000  times  the  sphere  we  have  taken  as  our 
unit,  We  find  the  distance  of  the  surface  of  this 

68 


THE  EXTENT  OF  THE  UNIVERSE 

sphere  by  extracting  the  cube  root  of  this  number, 
which  gives  us  500.  We  may,  therefore,  say,  as  the 
result  of  a  very  rough  estimate,  that  the  number  of 
stars  we  have  supposed  would  be  contained  within 
a  distance  found  by  multiplying  400,000  times  the 
distance  of  the  sun  by  500 ;  that  is,  that  they  are  con- 
tained within  a  region  whose  boundary  is  200,000,000 
times  the  distance  of  the  sun.  This  is  a  distance 
through  which  light  would  travel  in  about  3300  years. 

It  is  not  impossible  that  the  number  of  stars  is 
much  greater  than  that  we  have  supposed.  Let 
us  grant  that  there  are  eight  times  as  many,  or 
1,000,000,000.  Then  we  should  have  to  extend  the 
boundary  of  our  universe  twice  as  far,  carrying  it 
to  a  distance  which  light  would  require  6600  years 
to  travel. 

There  is  another  method  of  estimating  the  thick- 
ness with  which  stars  are  sown  through  space,  and 
hence  the  extent  of  the  universe,  the  result  of  which 
will  be  of  interest.  It  is  based  on  the  proper  motion 
of  the  stars.  One  of  the  greatest  triumphs  of  astron- 
omy of  our  time  has  been  the  measurement  of  the 
actual  speed  at  which  many  of  the  stars  are  moving 
to  or  from  us  in  space.  These  measures  are  made 
with  the  spectroscope.  Unfortunately,  they  can  be 
best  made  only  on  the  brighter  stars — becoming  very 
difficult  in  the  case  of  stars  not  plainly  visible  to  the 
naked  eye.  Still  the  motions  of  several  hundreds 
have  been  measured  and  the  number  is  constantly 
increasing. 

A  general  result  of  all  these  measures  and  of  other 
estimates  may  be  summed  up  by  saying  that  there 
is  a  certain  average  speed  with  which  the  individ- 
ual stars  move  in  space;  and  that  this  average  is 

69 


SIDE-LIGHTS     ON    ASTRONOMY 

about  twenty  miles  per  second.  We  are  also  able 
to  form  an  estimate  as  to  what  proportion  of  the 
stars  move  with  each  rate  of  speed  from  the  lowest 
up  to  a  limit  which  is  probably  as  high  as  150 
miles  per  second.  Knowing  these  proportions  we 
have,  by  observation  of  the  proper  motions  of  the 
stars,  another  method  of  estimating  how  thickly  they 
are  scattered  in  space;  in  other  words,  what  is  the 
volume  of  space  which,  on  the  average,  contains  a 
single  star.  This  method  gives  a  thickness  of  the 
stars  greater  by  about  twenty -five  per  cent,  than 
that  derived  from  the  measures  of  parallax.  That 
is  to  say,  a  sphere  like  the  second  we  have  pro- 
posed, having  a  radius  800,000  times  the  distance 
of  the  sun,  and  therefore  a  diameter  1,600,000  times 
this  distance,  would,  judging  by  the  proper  motions, 
have  ten  or  twelve  stars  contained  within  it,  while 
the  measures  of  parallax  only  show  eight  stars  within 
the  sphere  of  this  diameter  having  the  sun  as  its 
centre.  The  probabilities  are  in  favor  of  the  result 
giving  the  greater  thickness  of  the  stars.  But,  after 
all,  the  discrepancy  does  not  change  the  general  con- 
clusion as  to  the  limits  of  the  visible  universe.  If  we 
cannot  estimate  its  extent  with  the  same  certainty 
that  we  can  determine  the  size  of  the  earth,  we  can 
still  form  a  general  idea  of  it. 

The  estimates  we  have  made  are  based  on  the  sup- 
position that  the  stars  are  equally  scattered  in  space. 
We  have  good  reason  to  believe  that  this  is  true  of  all 
the  stars  except  those  of  the  Milky  Way.  But,  after 
all,  the  latter  probably  includes  half  the  whole  num- 
ber of  stars  visible  with  a  telescope,  and  the  question 
may  arise  whether  our  results  are  seriously  wrong 
from  this  cause.  This  question  can  best  be  solved 

70 


THE  EXTENT  OF  THE  UNIVERSE 

by  yet  another  method  of  estimating  the  average 
distance  of  certain  classes  of  stars. 

The  parallaxes  of  which  we  have  heretofore  spoken 
consist  in  the  change  in  the  direction  of  a  star  pro- 
duced by  the  swing  of  the  earth  from  one  side  of  its 
orbit  to  the  other.  But  we  have  already  remarked 
that  our  solar  system,  with  the  earth  as  one  of  its 
bodies,  has  been  journeying  straightforward  through 
space  during  all  historic  times.  It  follows,  therefore, 
that  we  are  continually  changing  the  position  from 
which  we  view  the  stars,  and  that,  if  the  latter  were 
at  rest,  we  could,  by  measuring  the  apparent  speed 
with  which  they  are  moving  in  the  opposite  direction 
from  that  of  the  earth,  determine  their  distance.  But 
since  every  star  has  its  own  motion,  it  is  impossible, 
in  any  one  case,  to  determine  how  much  of  the  ap- 
parent motion  is  due  to  the  star  itself,  and  how  much 
to  the  motion  of  the  solar  system  through  space. 
Yet,  by  taking  general  averages  among  groups  of 
stars,  most  of  which  are  probably  near  each  other, 
it  is  possible  to  estimate  the  average  distance  by  this 
method.  When  an  attempt  is  made  to  apply  it,  so 
as  to  obtain  a  definite  result,  the  astronomer  finds 
that  the  data  now  available  for  the  purpose  are  very 
deficient.  The  proper  motion  of  a  star  can  be  deter- 
mined only  by  comparing  its  observed  position  in  the 
heavens  at  two  widely  separate  epochs.  Observa- 
tions of  sufficient  precision  for  this  purpose  were  com- 
menced about  1750  at  the  Greenwich  Observatory, 
by  Bradley,  then  Astronomer  Royal  of  England.  But 
out  of  3000  stars  which  he  determined,  only  a  few 
are  available  for  the  purpose.  Even  since  his  time, 
the  determinations  made  by  each  generation  of  as- 
tronomers have  not  been  sufficiently  complete  and 

6  71 


SIDE-LIGHTS    ON    ASTRONOMY 

systematic  to  furnish  the  material  for  anything  like 
a  precise  determination  of  the  proper  motions  of 
stars.  To  determine  a  single  position  of  any  one  star 
involves  a  good  deal  of  computation,  and  if  we  re- 
flect that,  in  order  to  attack  the  problem  in  question 
in  a  satisfactory  way,  we  should  have  observations  of 
1,000,000  of  these  bodies  made  at  intervals  of  at  least 
a  considerable  fraction  of  a  century,  we  see  what  an 
enormous  task  the  astronomers  dealing  with  this  prob- 
lem have  before  them,  and  how  imperfect  must  be 
any  determination  of  the  distance  of  the  stars  based 
on  our  motion  through  space.  So  far  as  an  estimate 
can  be  made,  it  seems  to  agree  fairly  well  with  the 
results  obtained  by  the  other  methods.  Speaking 
roughly,  we  have  reason,  from  the  data  so  far  avail- 
able, to  believe  that  the  stars  of  the  Milky  Way  are 
situated  at  a  distance  between  100,000,000  and  200,- 
000,000  times  the  distance  of  the  sun.  At  distances 
less  than  this  it  seems  likely  that  the  stars  are  dis- 
tributed through  space  with  some  approach  to  uni- 
formity. We  may  state  as  a  general  conclusion,  in- 
dicated by  several  methods  of  making  the  estimate, 
that  nearly  all  the  stars  which  we  can  see  with  our 
telescopes  are  contained  within  a  sphere  not  likely 
to  be  much  more  than  200,000,000  times  the  dis- 
tance of  the  sun. 

The  inquiring  reader  may  here  ask  another  ques- 
tion. Granting  that  all  the  stars  we  can  see  are 
contained  within  this  limit,  may  there  not  be  any 
number  of  stars  outside  the  limit  which  are  invisible 
only  because  they  are  too  far  away  to  be  seen? 

This  question  may  be  answered  quite  definitely 
if  we  grant  that  light  from  the  most  distant  stars 
meets  with  no  obstruction  in  reaching  us.  The  most 

72 


THE    EXTENT    OF    THE    UNIVERSE 

conclusive  answer  is  afforded  by  the  measure  of 
starlight.  If  the  stars  extended  out  indefinitely, 
then  the  number  of  those  of  each  order  of  magnitude 
would  be  nearly  four  times  that  of  the  magnitude 
next  brighter.  For  example,  we  should  have  nearly 
four  times  as  many  stars  of  the  sixth  magnitude  as 
of  the  fifth ;  nearly  four  times  as  many  of  the  seventh 
as  of  the  sixth,  and  so  on  indefinitely.  Now,  it  is 
actually  found  that  while  this  ratio  of  increase  is 
true  for  the  brighter  stars,  it  is  not  so  for  the  fainter 
ones,  and  that  the  increase  in  the  number  of  the 
latter  rapidly  falls  off  when  we  make  counts  of  the 
fainter  telescopic  stars.  In  fact,  it  has  long  been 
known  that,  were  the  universe  infinite  in  extent,  and 
the  stars  equally  scattered  through  all  space,  the 
whole  heavens  would  blaze  with  the  light  of  count- 
less millions  of  distant  stars  separately  invisible  even 
with  the  telescope. 

The  only  way  in  which  this  conclusion  can  be  in- 
validated is  by  the  possibility  that  the  light  of  the 
stars  is  in  some  way  extinguished  or  obstructed  in 
its  passage  through  space.  A  theory  to  this  effect 
was  propounded  by  Struve  nearly  a  century  ago, 
but  it  has  since  been  found  that  the  facts  as  he  set 
them  forth  do  not  justify  the  conclusion,  which  was, 
in  fact,  rather  hypothetical.  The  theories  of  modern 
science  converge  towards  the  view  that,  in  the  pure 
ether  of  space,  no  single  ray  of  light  can  ever  be  lost, 
no  matter  how  far  it  may  travel.  But  there  is  an- 
other possible  cause  for  the  extinction  of  light.  Dur- 
ing the  last  few  years  discoveries  of  dark  and  there- 
fore invisible  stars  have  been  made  by  means  of  the 
spectroscope  with  a  success  which  would  have  been 
quite  incredible  a  very  few  years  ago,  and  which,  even 

73 


SIDE-LIGHTS    ON    ASTRONOMY 

to-day,  must  excite  wonder  and  admiration.  The 
general  conclusion  is  that,  besides  the  shining  stars 
which  exist  in  space,  there  may  be  any  number  of 
dark  ones,  forever  invisible  in  our  telescopes.  May 
it  not  be  that  these  bodies  are  so  numerous  as  to  cut 
off  the  light  which  we  would  otherwise  receive  from 
the  more  distant  bodies  of  the  universe?  It  is,  of 
course,  impossible  to  answer  this  question  in  a  posi- 
tive way,  but  the  probable  conclusion  is  a  negative 
one.  We  may  say  with  certainty  that  dark  stars  are 
not  so  numerous  as  to  cut  off  any  important  part  of 
the  light  from  the  stars  of  the  Milky  Way,  because, 
if  they  did,  the  latter  would  not  be  so  clearly  seen  as 
it  is.  Since  we  have  reason  to  believe  that  the  Milky 
Way  comprises  the  more  distant  stars  of  our  system, 
we  may  feel  fairly  confident  that  not  much  light  can 
be  cut  off  by  dark  bodies  from  the  most  distant 
region  to  which  our  telescopes  can  penetrate.  Up 
to  this  distance  we  see  the  stars  just  as  they  are. 
Even  within  the  limit  of  the  universe  as  we  under- 
stand it,  it  is  likely  that  more  than  one-half  the  stars 
which  actually  exist  are  too  faint  to  be  seen  by  hu- 
man vision,  even  when  armed  with  the  most  powerful 
telescopes.  But  their  invisibility  is  due  only  to  their 
distance  and  the  faintness  of  their  intrinsic  light, 
and  not  to  any  obstructing  agency. 

The  possibility  of  dark  stars,  therefore,  does  not 
invalidate  the  general  conclusions  at  which  our  sur- 
vey of  the  subject  points.  The  universe,  so  far  as 
we  can  see  it,  is  a  bounded  whole.  It  is  surrounded 
by  an  immense  girdle  of  stars,  which,  to  our  vision, 
appears  as  the  Milky  Way.  While  we  cannot  set 
exact  limits  to  its  distance,  we  may  yet  confidently 
say  that  it  is  bounded.  It  has  uniformities  running 

74 


THE    EXTENT    OF    THE    UNIVERSE 

through  its  vast  extent.  Could  we  fly  out  to  dis- 
tances equal  to  that  of  the  Milky  Way,  we  should 
find  comparatively  few  stars  beyond  the  limits  of 
that  girdle.  It  is  true  that  we  cannot  set  any  defi- 
nite limit  and  say  that  beyond  this  nothing  exists. 
What  we  can  say  is  that  the  region  containing  the 
visible  stars  has  some  approximation  to  a  boundary. 
We  may  fairly  anticipate  that  each  successive  genera- 
tion of  astronomers,  through  coming  centuries,  will 
obtain  a  little  more  light  on  the  subject — will  be 
enabled  to  make  more  definite  the  boundaries  of  our 
system  of  stars,  and  to  draw  more  and  more  probable 
conclusions  as  to  the  existence  or  non-existence  of 
any  object  outside  of  it.  The  wise  investigator  of 
to-day  will  leave  to  them  the  task  of  putting  the 
problem  into  a  more  positive  shape. 


V 

MAKING   AND   USING  A  TELESCOPE 

THE  impression  is  quite  common  that  satisfactory 
views  of  the  heavenly  bodies  can  be  obtained 
only  with  very  large  telescopes,  and  that  the  owner 
of  a  small  one  must  stand  at  a  great  disadvantage 
alongside  of  the  fortunate  possessor  of  a  great  one. 
This  is  not  true  to  the  extent  commonly  supposed. 
Sir  William  Herschel  would  have  been  delighted  to 
view  the  moon  through  what  we  should  now  consider 
a  very  modest  instrument;  and  there  are  some  ob- 
jects, especially  the  moon,  which  commonly  present  a 
more  pleasing  aspect  through  a  small  telescope  than 
through  a  large  one.  The  numerous  owners  of  small 
telescopes  throughout  the  country  might  find  their  in- 
struments much  more  interesting  than  they  do  if  they 
only  knew  what  objects  were  best  suited  to  examina- 
tion with  the  means  at  their  command.  There  are 
many  others,  not  possessors  of  telescopes,  who  would 
like  to  know  how  one  can  be  acquired,  and  to  whom 
hints  in  this  direction  will  be  valuable.  We  shall 
therefore  give  such  information  as  we  are  able  re- 
specting the  construction  of  a  telescope,  and  the 
more  interesting  celestial  objects  to  which  it  may  be 
applied. 

Whether  the  reader  does  or  does  not  feel  com- 
petent to  undertake  the  making  of  a  telescope,  it  may 

76 


MAKING   AND    USING    A    TELESCOPE 

be  of  interest  to  him  to  know  how  it  is  done.  First, 
as  to  the  general  principles  involved,  it  is  generally 
known  that  the  really  vital  parts  of  the  telescope, 
which  by  their  combined  action  perform  the  office 
of  magnifying  the  object  looked  at,  are  two  in  num- 
ber, the  objective  and  the  eye -piece.  The  former 
brings  the  rays  of  light  which  emanate  from  the  ob- 
ject to  the  focus  where  the  image  of  the  object  is 
formed.  The  eye-piece  enables  the  observer  to  see 
this  image  to  the  best  advantage. 

The  functions  of  the  objective  as  well  as  those  of 
the  eye-piece  may,  to  a  certain  extent,  each  be  per- 
formed by  a  single  lens.  Galileo  and  his  contempo- 
raries made  their  telescopes  in  this  way,  because  they 
knew  of  no  way  in  which  two  lenses  could  be  made  to 
do  better  than  one.  But  every  one  who  has  studied 
optics  knows  that  white  light  passing  through  a 
single  lens  is  not  all  brought  to  the  same  focus,  but 
that  the  blue  light  will  come  to  a  focus  nearer  the 
objective  than  the  red  light.  There  will,  in  fact,  be 
a  succession  of  images,  blue,  green,  yellow,  and  red, 
corresponding  to  the  colors  of  the  spectrum.  It  is 
impossible  to  see  these  different  images  clearly  at  the 
same  time,  because  each  of  them  will  render  all  the 
others  indistinct. 

The  achromatic  object-glass,  invented  by  Dollond, 
about  1750,  obviates  this  difficulty,  and  brings  all  the 
rays  to  nearly  the  same  focus.  Nearly  every  one  in- 
terested in  the  subject  is  aware  that  this  object-glass 
is  composed  of  two  lenses — a  concave  one  of  flint- 
glass  and  a  convex  one  of  crown-glass,  the  latter 
being  on  the  side  towards  the  object.  This  is  the 
one  vital  part  of  the  telescope,  the  construction  of 
which  involves  the  greatest  difficulty.  Once  in  pos- 

77  * 


SIDE-LIGHTS    ON    ASTRONOMY 

session  of  a  perfect  object-glass,  the  rest  of  the  tele- 
scope is  a  matter  of  little  more  than  constructive  skill 
which  there  is  no  difficulty  in  commanding. 

The  construction  of  the  object-glass  requires  two 
completely  distinct  processes :  the  making  of  the  rough 
glass,  which  is  the  work  of  the  glass-maker;  and  the 
grinding  and  polishing  into  shape,  which  is  the  work 
of  the  optician.  The  ordinary  glass  of  commerce 
will  not  answer  the  purpose  of  the  telescope  at  all, 
because  it  is  not  sufficiently  clear  and  homogeneous. 
Optical  glass,  as  it  is  called,  must  be  made  of  ma- 
terials selected  and  purified  with  the  greatest  care, 
and  worked  in  a  more  elaborate  manner  than  is  neces- 
sary in  any  other  kind  of  glass.  In  the  time  of  Dol- 
lond  it  was  found  scarcely  possible  to  make  good 
disks  of  flint-glass  more  than  three  or  four  inches  in 
diameter.  Early  in  the  present  century,  Guinand, 
of  Switzerland,  invented  a  process  by  which  disks  of 
much  larger  size  could  be  produced.  In  conjunction 
with  the  celebrated  Fraunhofer  he  made  disks  of  nine 
or  ten  inches  in  diameter,  which  were  employed  by 
his  colaborer  in  constructing  the  telescopes  which 
were  so  famous  in  their  time.  He  was  long  supposed 
to  be  in  possession  of  some  secret  method  of  avoid- 
ing the  difficulties  which  his  predecessors  had  met. 
It  is  now  believed  that  this  secret,  if  one  it  was,  con- 
sisted principally  in  the  constant  stirring  of  the 
molten  glass  during  the  process  of  manufacture. 
However  this  may  be,  it  is  a  curious  historical  fact 
that  the  most  successful  makers  of  these  great  disks 
of  glass  have  either  been  of  the  family  of  Guinand, 
or  successors,  in  the  management  of  the  family  firm. 
It  was  Feil,  a  son-in-law  or  near  relative,  who  made 
the  glass  from  which  Clark  fabricated  the  lenses  of 

78 


MAKING    AND    USING   A    TELESCOPE 

the  great  telescope  of  the  Lick  Observatory.  His 
successor,  Mantois,  of  Paris,  carried  the  art  to  a  point 
of  perfection  never  before  approached.  The  trans- 
parency and  uniformity  of  his  disks  as  well  as  the 
great  size  to  which  he  was  able  to  carry  them  would 
suggest  that  he  and  his  successors  have  out-distanced 
all  competitors  in  the  process.  He  it  was  who  made 
the  great  40-inch  lens  for  the  Yerkes  Observatory. 

As  optical  glass  is  now  made,  the  material  is  con- 
stantly stirred  with  an  iron  rod  during  all  the  time  it 
is  melting  in  the  furnace,  and  after  it  has  begun  to  cool, 
until  it  becomes  so  stiff  that  the  stirring  has  to  cease. 
It  is  then  placed,  pot  and  all,  in  the  annealing  furnace, 
where  it  is  kept  nearly  at  a  melting  heat  for  three 
weeks  or  more,  according  to  the  size  of  the  pot. 
When  the  furnace  has  cooled  off,  the  glass  is  taken 
out,  and  the  pot  is  broken  from  around  it,  leaving 
only  the  central  mass  of  glass.  Having  such  a  mass, 
there  is  no  trouble  in  breaking  it  up  into  pieces  of  all 
desirable  purity,  and  sufficiently  large  for  moderate- 
sized  telescopes.  But  when  a  great  telescope  of  two 
feet  aperture  or  upward  is  to  be  constructed,  very- 
delicate  and  laborious  operations  have  to  be  under- 
taken. The  outside  of  the  glass  has  first  to  be  chipped 
off,  because  it  is  filled  with  impurities  from  the  ma- 
terial of  the  pot  itself.  But  this  is  not  all.  Veins  of 
unequal  density  are  always  found  extending  through 
the  interior  of  the  mass,  no  way  of  avoiding  them 
having  yet  been  discovered.  They  are  supposed  to 
arise  from  the  materials  of  the  pot  and  stirring  rod, 
which  become  mixed  in  with  the  glass  in  consequence 
of  the  intense  heat  to  which  all  are  subjected.  These 
veins  must,  so  far  as  possible,  be  ground  or  chipped 
out  with  the  greatest  care.  The  glass  is  then  melted 

79 


SIDE-LIGHTS    ON    ASTRONOMY 

again,  pressed  into  a  flat  disk,  and  once  more  put  into 
the  annealing  oven.  In  fact,  the  operation  of  an- 
nealing must  be  repeated  every  time  the  glass  is 
melted.  When  cooled,  it  is  again  examined  for  veins, 
of  which  great  numbers  are  sure  to  be  found.  The 


THE    GLASS    DISK 

problem  now  is  to  remove  these  by  cutting  and  grind- 
ing without  either  breaking  the  glass  in  two  or  cutting 
a  hole  through  it.  If  the  parts  of  the  glass  are  once 
separated,  they  can  never  be  joined  without  producing 
a  bad  scar  at  the  point  of  junction.  So  long,  how- 
ever, as  the  surface  is  unbroken,  the  interior  parts  of 
the  glass  can  be  changed  in  form  to  any  extent. 
Having  ground  out  the  veins  as  far  as  possible,  the 
glass  is  to  be  again  melted,  and  moulded  into  proper 
shape.  In  this  mould  great  care  must  be  taken  to 
have  no  folding  of  the  surface.  Imagining  the  latter 
to  be  a  sort  of  skin  enclosing  the  melted  glass  inside, 
it  must  be  raised  up  wherever  the  glass  is  thinnest, 
and  the  latter  allowed  to  slowly  run  together  be- 
neath it. 

If  the  disk  is  of  flint,  all  the  veins  must  be  ground 
out  on  the  first  or  second  trial,  because  after  two  or 
three  mouldings  the  glass  will  lose  its  transparency. 
A  crown  disk  may,  however,  be  melted  a  number  of 

80 


MAKING    AND    USING    A    TELESCOPE 

times  without  serious  injury.  In  many  cases — per- 
haps the  majority — the  artisan  finds  that  after  all 
his  months  of  labor  he  cannot  perfectly  clear  his  glass 
of  the  noxious  veins,  and  he  has  to  break  it  up  into 
smaller  pieces.  When  he  finally  succeeds,  the  disk 
has  the  form  of  a  thin  grindstone  two  feet  or  upward 
in  diameter,  according  to  the  size  of  the  telescope  to 
be  made,  and  from  two  to  three  inches  in  thickness. 
The  glass  is  then  ready  for  the  optician. 

The  first  process  to  be  performed  by  the  optician 
is  to  grind  the  glass  into  the  shape  of  a  lens  with 
perfectly  spherical  surfaces.  The  convex  surface 


THE  OPTICIAN'S  TOOL 

must  be  ground  in  a  saucer-shaped  tool  of  correspond- 
ing form.  It  is  impossible  to  make  a  tool  perfectly 
spherical  in  the  first  place,  but  success  may  be  se- 
cured on  the  geometrical  principle  that  two  surfaces 

81 


SIDE-LIGHTS    ON    ASTRONOMY 

cannot  fit  each  other  in  all  positions  unless  both  are 
perfectly  spherical.  The  tool  of  the  optician  is  a 
very  simple  affair,  being  nothing  more  than  a  plate 
of  iron  somewhat  larger,  perhaps  a  fourth,  than  the 
lens  to  be  ground  to  the  corresponding  curvature. 
In  order  to  insure  its  changing  to  fit  the  glass,  it  is 


THE    OPTICIAN  S    TOOL 


covered  on  the  interior  with  a  coating  of  pitch  from 
an  eighth  to  a  quarter  of  an  inch  thick.  This  ma- 
terial is  admirably  adapted  to  the  purpose  because  it 
gives  way  certainly,  though  very  slowly,  to  the  press- 
ure of  the  glass.  In  order  that  it  may  have  room  to 
change  its  form,  grooves  are  cut  through  it  in  both 
directions,  so  as  to  leave  it  in  the  form  of  squares, 
like  those  on  a  chess-board. 

It  is  then  sprinkled  over  with  rouge,  moistened 
with  water,  and  gently  warmed.  The  roughly  ground 
lens  is  then  placed  upon  it,  and  moved  from  side  to 
side.  The  direction  of  the  motion  is  slightly  changed 
with  every  stroke,  so  that  fter  a  dozen  or  so  of 
strokes  the  lines  of  motion  will  lie  in  every  direction 
on  the  tool.  This  change  of  direction  is  most  readily 
and  easily  effected  by  the  operator  slowly  walking 
around  as  he  polishes,  at  the  same  time  the  lens  is 
to  be  slowly  turned  around  either  in  the  opposite 
direction  or  more  rapidly  yet  in  the  same  direction, 

82 


MAKING    AND    USING    A    TELESCOPE 

so  that  the  strokes  of  the  polisher  shall  cross  the  lens 
in  all  directions.  This  double  motion  insures  every 
part  of  the  lens  coming  into  contact  with  every  part 
of  the  polisher,  and  moving  over  it  in  every  direction. 

Then  whatever  parts  either  of  the  lens  or  of  the 
polisher  may  be  too  high  to  form  a  spherical  surface 
will  be  gradually  worn  down,  thus  securing  the  per- 
fect sphericity  of  both. 

When  the  polishing  is  done  by  machinery,  which 
is  the  custom  in  Europe,  with  large  lenses,  the  polisher 


GRINDING    A    LARGE    LENS 

is  slid  back  and  forth  over  the  lens  by  means  of  a 
crank  attached  to  a  revolving  wheel.  The  polisher 
is  at  the  same  time  slowly  revolving  around  a  pivot 
at  its  centre,  which  pivot  the  crank  works  into,  and 
the  glass  below  it  is  slo\\ly  turned  in  an  opposite  di- 
rection. Thus  the  same  effect  is  produced  as  in  the 
other  system.  Those  who  practice  this  method  claim 

83 


SIDE-LIGHTS    ON    ASTRONOMY 

that  by  thus  using  machinery  the  conditions  of  a 
uniform  polish  for  every  part  of  the  surface  can  be 
more  perfectly  fulfilled  than  by  a  hand  motion.  The 
results,  however,  do  not  support  this  view.  No 
European  optician  will  claim  to  do  better  than  the 
American  firm  of  Alvan  Clark  &  Sons  in  producing 
uniformly  good  object-glasses,  and  this  firm  always 
does  the  work  by  hand,  moving  the  glass  over  the 
polisher,  and  not  the  polisher  over  the  glass. 

Having  brought  both  flint  and  crown  glasses  into 
proper  figure  by  this  process,  they  are  joined  together, 
and  tested  by  observations  either  upon  a  star  in  the 
heavens,  or  some  illuminated  point  at  a  little  distance 
on  the  ground.  The  reflection  of  the  sun  from  a  drop 
of  quicksilver,  a  thermometer  bulb,  or  even  a  piece 
of  broken  bottle,  makes  an  excellent  artificial  star. 
The  very  best  optician  will  always  find  that  on  a  first 
trial  his  glass  is  not  perfect.  He  will  find  that  he 
has  not  given  exactly  the  proper  curves  to  secure 
achromatism.  He  must  then  change  the  figure  of 
one  or  both  the  glasses  by  polishing  it  upon  a  tool  of 
slightly  different  curvature.  He  may  also  find  that 
there  is  some  spherical  aberration  outstanding.  He 
must  then  alter  his  curve  so  as  to  correct  this.  The 
correction  of  these  little  imperfections  in  the  figures 
of  the  lenses  so  as  to  secure  perfect  vision  through 
them  is  the  most  difficult  branch  of  the  art  of  the 
optician,  and  upon  his  skill  in  practising  it  will  de- 
pend more  than  upon  anything  else  his  ultimate  suc- 
cess and  reputation.  The  shaping  of  a  pair  of  lenses 
in  the  way  we  have  described  is  not  beyond  the  power 
of  any  person  of  ordinary  mechanical  ingenuity,  pos- 
sessing the  necessary  delicacy  of  touch  and  apprecia- 
tion of  the  problem  he  is  attacking.  But  to  make  a 

84 


MAKING    AND    USING    A    TELESCOPE 

perfect  objective  of  considerable  size,  which  shall 
satisfy  all  the  wants  of  the  astronomer,  is  an  under- 
taking requiring  such  accuracy  of  eyesight,  and 
judgment  in  determining  where  the  error  lies,  and 
such  skill  in  manipulating  so  as  to  remove  the  de- 
fects, that  the  successful  men  in  any  one  generation 
can  be  counted  on  one's  fingers. 

In  order  that  the  telescope  may  finally  perform 
satisfactorily  it  is  not  sufficient  that  the  lenses  should 
both  be  of  proper  figure ;  they  must  also  both  be  prop- 
erly centred  in  their  cells.  If  either  lens  is  tipped 
aside,  or  slid  out  from  its  proper  central  line,  the  defi- 
nition will  be  injured.  As  this  is  liable  to  happen 
with  almost  any  telescope,  we  shall  explain  how  the 
proper  adjustment  is  to  be  made. 

The  easiest  way  to  test  this  adjustment  is  to  set 
the  cell  with  the  two  glasses  of  the  objective  in  it 
against  a  wall  at  night,  and  going  to  a  short  distance, 
observe  the  reflection  in  the  glass  of  the  flame  of  a 
candle  held  in  the  hand.  Three  or  four  reflections 
will  be  seen  from  the  different  surfaces.  The  ob- 
server, holding  the  candle  before  his  eye,  and  having 
his  line  of  sight  as  close  as  possible  to  the  flame,  must 
then  move  until  the  different  images  of  the  flame 
coincide  with  each  other.  If  he  cannot  bring  them 
into  coincidence,  owing  to  different  pairs  coinciding 
on  different  sides  of  the  flame,  the  glasses  are  not 
perfectly  centred  upon  each  other.  When  the  cen- 
tring is  perfect,  the  observer  having  the  light  in  the 
line  of  the  axes  of  the  lenses,  and  (if  it  were  possible 
to  do  so)  looking  through  the  centre  of  the  flame, 
would  see  the  three  or  four  images  all  in  coincidence. 
As  he  cannot  see  through  the  flame  itself,  he  must 
look  first  on  one  side  and  then  on  the  other,  and  see 

85 


SIDE-LIGHTS    ON    ASTRONOMY 

if  the  arrangement  of  the  images  seen  in  the  lenses 
is  symmetrical.  If,  going  to  different  distances,  he 
finds  no  deviation  from  symmetry,  in  this  respect  the 
adjustment  is  near  enough  for  all  practical  purposes. 
A  more  artistic  instrument  than  a  simple  candle  is 
a  small  concave  reflector  pierced  through  its  centre, 
such  as  is  used  by  physicians  in  examining  the  throat. 


IMAGE    OF   CANDLE-FLAME 
IN    OBJECT-GLASS 


TESTING   ADJUSTMENT 
OF   OBJECT-GLASS 


Place  this  reflector  in  the  prolongation  of  the  optical 
axis,  set  the  candle  so  that  the  light  from  the  re- 
flector shall  be  shown  through  the  glass,  and  look 
through  the  opening.  Images  of  the  reflector  itself 
will  then  be  seen  in  the  object-glass,  and  if  the  ad- 
justment is  perfect,  the  reflector  can  be  moved  so 
that  they  will  all  come  into  coincidence  together. 

When  the  objective  is  in  the  tube  of  the  telescope, 
it  is  always  well  to  examine  this  adjustment  from 
time  to  time,  holding  the  candle  so  that  its  light  shall 
shine  through  the  opening  perpendicularly  upon  the 
object-glass.  The  observer  looks  upon  one  side  of  the 

86 


MAKING    AND    USING    A    TELESCOPE 

flame,  and  then  upon  the  other,  to  see  if  the  images 
are  symmetrical  in  the  different  positions.  If  in  order 
to  see  them  in  this  way  the  candle  has  to  be  moved 
to  one  side  of  the  central  line  of  the  tube,  the  whole 
objective  must  be  adjusted.  If  two  images  coincide 
in  one  position  of  the  candle-flame,  and  two  in  an- 
other position,  so  that  they  cannot  all  be  brought 
together  in  any  position,  it  shows  that  the  glasses 
are  not  properly  adjusted  in  their  cell.  It  may  be 
remarked  that  this  last  adjustment  is  the  proper 
work  of  the  optician,  since  it  is  so  difficult  that  the 
user  of  the  telescope  cannot  ordinarily  effect  it. 
But  the  perpendicularity  of  the  whole  objective  to 
the  tube  of  the  telescope  is  liable  to  be  deranged  in 
use,  and  every  one  who  uses  such  an  instrument 
should  be  able  to  rectify  an  error  of  this  kind. 

The  question  may  be  asked,  How  much  of  a  tele- 
scope can  an  amateur  observer,  under  any  circum- 
stances, make  for  himself?  As  a  general  rule,  his 
work  in  this  direction  must  be  confined  to  the  tube 
and  the  mounting.  We  should  not,  it  is  true,  dare 
to  assert  that  any  ingenious  young  man,  with  a  clear 
appreciation  of  optical  principles,  could  not  soon 
learn  to  grind  and  polish  an  object-glass  for  himself 
by  the  method  we  have  described,  and  thus  obtain 
a  much  better  instrument  than  Galileo  ever  had  at 
his  command.  But  it  would  be  a  wonderful  success 
if  his  home-made  telescope  was  equal  to  the  most 
indifferent  one  which  can  be  bought  at  an  optician's. 
The  objective,  complete  in  itself,  can  be  purchased  at 
prices  depending  upon  the  size.* 

*  The  following  is  a  rough  rule  for  getting  an  idea  of  the  price  of 
an  achromatic  objective,  made  to  order,  of  the  finest  quality.  Take 
the  cube  of  the  diameter  in  inches,  or.  which  is  the  same  thing, 


SIDE-LIGHTS    ON    ASTRONOMY 

The  tube  for  the  telescope  may  be  made  of  paper, 
by  pasting  a  great  number  of  thicknesses  around  a 
long  wooden  cylinder.  A  yet  better  tube  is  made  of 
a  simple  wooden  box.  The.  best  material,  however,  is 
metal,  because  wood  and  pasteboard  are  liable  both 
to  get  out  of  shape,  and  to  swell  under  the  influence 
of  moisture.  Tin,  if  it  be  of  sufficient  thickness, 
would  be  a  very  good  material.  The  brighter  it  is 


A    VERY    PRIMITIVE    MOUNTING    FOR    A    TELESCOPE 

kept,  the  better.  The  work  of  fitting  the  objective 
into  one  end  of  a  tin  tube  of  double  thickness,  and 
properly  adjusting  it,  will  probably  be  quite  within 
the  powers  of 'the  ordinary  amateur.  The  fitting  of 

calculate  the  contents  of  a  cubical  box  which  would  hold  a  sphere 
of  the  same  diameter  as  the  clear  aperture  of  the  glass.  The 
price  of  the  glass  will  then  range  from  $i  to  $i  75  for  each  cubic 
inch  in  this  box.  For  example,  the  price  of  a  four-inch  objective 
will  probably  range  from  $64  to  $112.  Very  small  object-glasses 
of  one  or  two  inches  may  be  a  little  higher  than  would  be  given 
by  this  rule.  Instruments  which  are  not  first-class,  but  will  an- 
swer most  of  the  purposes  of  the  amateur,  are  much  cheaper. 

88 


MAKING    AND    USING    A    TELESCOPE 

the  eye-piece  into  the  other  end  of  the  tube  will  re- 
quire some  skill  and  care  both  on  his  own  part  and 
that  of  his  tinsmith. 

Although  the  construction  of  the  eye-piece  is  much 
easier  than  that  of  the  objective,  since  the  same  ac- 
curacy in  adjusting  the  curves  is  not  necessary,  yet 
the  price  is  lower  in  a  yet  greater  degree,  so  that 
the  amateur  will  find  it  better  to  - 
buy  than  to  make  his  eye -piece, 
unless  he  is  anxious  to  test  his  me- 
chanical powers.  For  a  telescope 
which  has  no  micrometer,  the  Huy- 

ghenian  or  negative  eye-piece,  as  it      

is   commonly    called,    is    the   best. 

As  made  by  Huyghens,  it  consists     TH\™-7iEcTAN 

of   two  piano  -  convex  lenses,  with 

their  plane  sides  next  the  eye,  as  shown  in  the  figure. 

So  far  as  we  have  yet  described  our  telescope  it  is 
optically  complete.  If  it  could  be  used  as  a  spy- 
glass by  simply  holding  it  in  the  hand,  and  pointing 
at  the  object  we  wish  to  observe,  there  would  be  lit- 
tle need  of  any  very  elaborate  support.  But  if  a 
telescope,  even  of  the  smallest  size,  is  to  be  used  with 
regularity,  a  proper  "mounting"  is  as  essential  as  a 
good  instrument.  Persons  unpractised  in  the  use  of 
such  instruments  are  very  apt  to  underrate  the  im- 
portance of  those  accessories  which  merely  enable 
us  to  point  the  telescope.  An  idea  of  what  is  wanted 
in  the  mounting  may  readily  be  formed  if  the  reader 
will  try  to  look  at  a  star  with  an  ordinary  good-sized 
spy-glass  held  in  the  hand,  and  then  imagine  the 
difficulties  he  meets  with  multiplied  by  fifty. 

The  smaller  and  cheaper  telescopes,  as  commonly 
sold,  are  mounted  on  a  simple  little  stand,  on  which 

89 


SIDE-LIGHTS    ON    ASTRONOMY 


the  instrument  admits  of  a  horizontal  and  vertical 
motion.  If  one  only  wants  to  get  a  few  glimpses  of 
a  celestial  object,  this  mounting  will  answer  his  pur- 
pose. But  to  make  anything  like  a  study  of  a  celestial 

body,  the  mounting  must 
be  an  equatorial  one; 
that  is,  one  of  the  axes 
around  which  the  tele- 
scope moves  must  be  in- 
clined so  as  to  point 
towards  the  pole  of  the 
heavens,  which  is  near 
the  polar  star.  This  axis 
will  then  make  an  angle 
with  the  horizon  equal 
to  the  latitude  of  the 
place.  The  telescope  can- 
not, however,  be  mount- 
ed directly  on  this  axis, 
but  must  be  attached  to 
a  second  one,  itself  fast- 
ened to  this  one. 

When  mounted  in  this 
way,  an   object   can  be 
followed    in    its   diurnal 
motion  from  east  to  west  by  turning  on  the  polar  axis 
alone.     But  if  the  greatest  facility  in  use  is  required,  j 
this  motion  must  be  performed  by  clock-work.     A 
telescope  with    this   appendage  will  commonly  cost 
one  thousand  dollars  and  upward,  so  that  it  is  not  1 
usually  applied  to  very  small  ones. 

We  will  now  suppose  that  the  reader  wishes  to 
purchase  a  telescope  or  an  object-glass  for  himself,  i 
and  to  be  able  to  judge  of  its  performance.     He  must 

90 


SECTION     OF     THE     PRIMITIVE 

MOUNTING 

P  P.  Polar  axis,  bearing  a  fork  at  the  upper  end 
A .  Declination  axis  passing  through  the  fork 
E.  Section  of  telescope  tube 
C.  Weight  to  balance  the  tube 


MAKING    AND    USING    A    TELESCOPE 

have  the  object-glass  properly  adjusted  in  its  tube, 
and  must  use  the  highest  power ;  that  is,  the  smallest 
eye-piece,  which  he  intends  to  use  in  the  instrument. 
Of  course  he  understands  that  in  looking  directly  at 
a  star  or  a  celestial  object  it  must  appear  sharp  in 
outline  and  well  defined.  But  without  long  practice 
with  good  instruments,  this  will  not  give  him  a  very 
definite  idea.  If  the  person  who  selects  the  telescope 
is  quite  unpractised,  it  is  possible  that  he  can  make 
the  best  test  by  ascertaining  at  what  distance  he  can 
read  ordinary  print.  To  do  this  he  should  have  an 
eye-piece  magnifying  about  fifty  times  for  each  inch 
of  aperture  of  the  telescope.  For  instance,  if  his 
telescope  is  three  inches  clear  aperture,  then  his  eye- 
piece should  magnify  one  hundred  and  fifty  times; 
if  the  aperture  is  four  inches,  one  magnifying  two 
hundred  times  may  be  used.  This  magnifying  power 
is,  as  a  general  rule,  about  the  highest  that  can 
be  advantageously  used  with  any  telescope.  Sup- 
posing this  magnifying  power  to  be  used,  this  page 
should  be  legible  at  a  distance  of  four  feet  for 
every  unit  of  magnifying  power  of  the  telescope. 
For  example,  with  a  power  of  100,  it  should  be 
legible  at  a  distance  of  400  feet;  with  a  power  of 
200,  at  800  feet,  and  so  on.  To  put  the  condition 
into  another  shape :  if  the  telescope  will  read  the  print 
at  a  distance  of  150  feet  for  each  inch  of  aperture 
with  the  best  magnifying  power,  its  performance  is 
at  least  not  very  bad.  If  the  magnifying  power  is 
less  than  would  be  given  by  this  rule,  the  telescope 
should  perform  a  little  better;  for  instance,  a  three- 
inch  telescope  with  a  power  of  60  should  make  this 
page  legible  at  a  distance  of  300  feet,  or  four  feet  for 
each  unit  of  power. 


SIDE-LIGHTS    ON    ASTRONOMY 

The  test  applied  by  the  optician  is  much  more 
exact,  and  also  more  easy.  He  points  the  instru- 
ment at  a  star,  or  at  the  reflection  of  the  sun's  rays 
from  a  small  round  piece  of  glass  or  a  globule  of  quick- 
silver several  hundred  yards  away,  and  ascertains 
whether  the  rays  are  all  brought  to  a  focus.  This  is 
not  done  by  simply  looking  at  the  star,  but  by  alter- 
nately pushing  the  eye-piece  in  beyond  the  point  of 
distinct  vision  and  drawing  it  out  past  the  point. 
In  this  way  the  image  of  the  star  will  appear,  not  as 
a  point,  but  as  a  round  disk  of  light.  If  the  telescope 
is  perfect,  this  disk  will  appear  round  and  of  uniform 
brightness  in  either  position  of  the  eye-piece.  But 
if  there  is  any  spherical  aberration  or  differences  of 
density  in  different  parts  of  the  glass,  the  image  will 
appear  distorted  in  various  ways.  If  the  spherical 
aberration  is  not  correct,  the  outer  rim  of  the  disk 
will  be  brighter  than  the  centre  when  the  eye-piece 
is  pushed  in,  and  the  centre  will  be  the  brighter  when 
it  is  drawn  out.  If  the  curves  of  the  glass  are  not 
even  all  around,  the  image  will  appear  oval  in  one  or 
the  other  position.  If  there  are  large  veins  of  un- 
equal density,  wings  or  notches  will  be  seen  on  the 
image.  If  the  atmosphere  is  steady,  the  image,  when 
the  eye-piece  is  pushed  in,  will  be  formed  of  a  great 
number  of  minute  rings  of  light.  If  the  glass  is  good, 
these  rings  will  be  round,  unbroken,  and  equally 
bright.  We  present  several  figures  showing  how  these 
spectral  images,  as  they  are  sometimes  called,  will 
appear;  first,  when  the  eye-piece  is  pushed  in,  and 
secondly,  when  it  is  drawn  out,  with  telescopes  of 
different  qualities. 

We  have  thus  far  spoken  only  of  the  refracting 
telescope,  because  it  is  the  kind  with  which  an  ob- 

92 


SPECTRAL  IMAGES  OF  STARS  ;  THE  UPPER  LINE  SHOWING  HOW 
THEY  APPEAR  WITH  THE  EYE -PIECE  PUSHED  INJ  THE  LOWER 
WITH  THE  EYE-PIECE  DRAWN  OUT 

A.  The  telescope  is  all  right. 

B.  Spherical  aberration  shown  by  the  light  and  dark  centre. 

C.  The  objective  is  not  spherical,  but  elliptical. 

D.  The  glass  not  uniform — a  very  bad  and  incurable  case. 

E.  One  side  of  the  objective  nearer  than  the  other.    Adjust  it. 


MAKING    AND    USING    A    TELESCOPE 

server  would  naturally  seek  to  supply  himself.  At 
the  same  time  there  is  little  doubt  that  the  construc- 
tion of  a  reflector  of  moderate  size  is  easier  than  that 
of  a  corresponding  refractor.  The  essential  part  of 
the  reflector  is  a  slightly  concave  mirror  of  any  metal 
which  will  bear  a  high  polish.  This  mirror  may  be 
ground  and  polished  in  the  same  way  as  a  lens,  only 
the  tool  must  be  convex. 

Of  late  years  it  has  become  very  common  to  make 
the  mirror  of  glass  and  to  cover  the^  reflecting  face 
with  an  exceedingly  thin  film  of  silver,  which  can  be 
polished  by  hand  in  a  few  minutes.  Such  a  mirror 
differs  from  our  ordinary  looking-glass  in  that  the 
coating  of  silver  is  put  on  the  front  surface,  so  that 
the  light  does  not  pass  through  the  glass.  Moreover, 
the  coating  of  silver  is  so  thin  as  to  be  almost  trans- 
parent: in  fact,  the  sun  may  be  seen  through  it  by 
direct  vision  as  a  faint  blue  object.  Silvered  glass 
reflectors  made  in  this  way  are  extensively  manu- 
factured in  London,  and  are  far  cheaper  than  refract- 
ing telescopes  of  corresponding  size.  Their  great 
drawback  is  the  want  of  permanence  in  the  silver  film. 
In  the  city  the  film  will  ordinarily  tarnish  in  a  few 
months  from  the  sulphurous  vapors  arising  from  gas- 
lights and  other  sources,  and  even  in  the  country  it 
is  very  difficult  to  preserve  the  mirror  from  the  con- 
tact of  everything  that  will  injure  it.  In  consequence, 
the  possessor  of  such  a  telescope,  if  he  wishes  to  keep 
it  in  order,  must  always  be  prepared  to  resilver  and 
repolish  it.  To  do  this  requires  such  careful  manip- 
ulation and  management  of  the  chemicals  that  it  is 
hardly  to  be  expected  that  an  amateur  will  take  the 
trouble  to  keep  his  telescope  in  order,  unless  he  has  a 
taste  for  chemistry  as  well  as  for  astronomy. 

93 


SIDE-LIGHTS    ON    ASTRONOMY 

The  curiosity  to  see  the  heavenly  bodies  through 
great  telescopes  is  so  wide-spread  that  we  are  apt  to 
forget  how  much  can  be  seen  and  done  with  small 
ones.  The  fact  is  that  a  large  proportion  of  the 
astronomical  observations  of  past  times  have  been 
made  with  what  we  should  now  regard  as  very  small 
instruments,  and  a  good  deal  of  the  solid  astronomical 
work  of  the  present  time  is  done  with  meridian  circles 
the  apertures  of  which  ordinarily  range  from  four  to 
eight  inches.  One  of  the  most  conspicuous  examples 
in  recent  times  of  how  a  moderate-sized  instrument 
may  be  utilized  is  afforded  by  the  discoveries  of 
double  stars  made  by  Mr.  S.  W.  Burnham,  of  Chicago. 
Provided  with  a  little  six-inch  telescope,  procured  at 
his  own  expense  from  the  Messrs.  Clark,  he  has  dis- 
covered many  hundred  double  stars  so  difficult  that 
they  had  escaped  the  scrutiny  of  Maedler  and  the 
Struves,  and  gained  for  himself  one  of  the  highest 
positions  among  the  astronomers  of  the  day  engaged 
in  the  observation  of  these  objects.  It  was  with  this 
little  instrument  that  on  Mount  Hamilton,  California 
— afterward  the  site  of  the  great  Lick  Observatory — 
he  discovered  forty-eight  new  double  stars,  which 
had  remained  unnoticed  by  all  previous  observers. 

First  among  the  objects  which  show  beautifully 
through  moderate  instruments  stands  the  moon. 
People  who  want  to  see  the  moon  at  an  observatory 
generally  make  the  mistake  of  looking  when  the  moon 
is  full,  and  asking  to  see  it  through  the  largest  tele- 
scope. Nothing  can  then  be  made  out  but  a  brilliant 
blaze  of  light,  mottled  with  dark  spots,  and  crossed 
by  irregular  bright  lines.  The  best  time  to  view  the 
moon  is  near  or  before  the  first  quarter,  or  when  she 
is  from  three  to  eight  days  old.  The  last  quarter  is 

94 


MAKING    AND    USING    A    TELESCOPE 

of  course  equally  favorable,  so  far  as  seeing  is  con- 
cerned, only  one  must  be  up  after  midnight  to  see 
her  in  that  position.  Seen  through  a  three  or  four 
inch  telescope,  a  day  or  two  before  the  first  quarter, 
about  half  an  hour  after  sunset,  and  with  a  magnify- 
ing power  between  fifty  and  one  hundred,  the  moon 
is  one  of  the  most  beautiful  objects  in  the  heavens. 
Twilight  softens  her  radiance  so  that  the  eye  is  not 
dazzled  as  it  will  be  when  the  sky  is  entirely  dark. 
The  general  aspect  she  then  presents  is  that  of  a 
hemisphere  of  beautiful  chased  silver  carved  out  in 
curious  round  patterns  with  a  more  than  human 
skill.  If,  however,  one  wishes  to  see  the  minute  de- 
tails of  the  lunar  surface,  in  which  many  of  our  as- 
tronomers are  now  so  deeply  interested,  he  must  use 
a  higher  magnifying  power.  The  general  beautiful 
effect  is  then  lessened,  but  more  details  are  seen. 
Still,  it  is  hardly  necessary  to  seek  for  a  very  large 
telescope  for  any  investigation  of  the  lunar  surface. 
I  very  much  doubt  whether  any  one  has  ever  seen 
anything  on  the  moon  which  could  not  be  made  out 
in  a  clear,  steady  atmosphere  with  a  six-inch  tele- 
scope of  the  first  class. 

Next  to  the  moon,  Saturn  is  among  the  most  beau- 
tiful of  celestial  objects.  Its  aspect,  however,  varies 
with  its  position  in  its  orbit.  Twice  in  the  course  of 
a  revolution,  which  occupies  nearly  thirty  years,  the 
rings  are  seen  edgewise,  and  for  a  few  days  are  in- 
visible even  in  a  powerful  telescope.  For  an  entire 
year  their  form  may  be  difficult  to  make  out  with  a 
small  telescope.  These  unfavorable  conditions  oc- 
cur in  1907  and  1921.  Between  these  dates,  especial- 
ly for  some  years  after  1910,  the  position  of  the 
planet  in  the  sky  will  be  the  most  favorable,  being 

95 


SIDE-LIGHTS    ON    ASTRONOMY 

in  northern  decimation,  near  its  perihelion,  and  hav- 
ing its  rings  widely  open.  We  all  know  that  Saturn 
is  plainly  visible  to  the  naked  eye,  shining  almost 
like  a  star  of  the  first  magnitude,  so  that  there  is  no 
difficulty  in  finding  it  if  one  knows  when  and  where 
to  look.  In  1906-1908  its  oppositions  occur  in  the 
month  of  September.  In  subsequent  years,  it  will 
occur  a  month  later  every  two  and  a  half  years. 
The  ring  can  be  seen  with  a  common,  good  spy-glass 
fastened  to  a  post  so  as  to  be  steady.  A  four  or  five- 
inch  telescope  will  show  most  of  the  satellites,  the 
division  in  the  ring,  and,  when  the  ring  is  well  opened, 
the  curious  dusky  ring  discovered  by  Bond.  This 
"crape  ring,"  as  it  is  commonly  called,  is  one  of  the 
most  singular  phenomena  presented  by  that  planet. 
It  might  be  interesting  to  the  amateur  astronomer 
with  a  keen  eye  and  a  telescope  of  four  inches  aper- 
ture or  upward  to  frequently  scrutinize  Saturn,  with 
a  view  of  detecting  any  extraordinary  eruptions  upon 
his  surface,  like  that  seen  by  Professor  Hall  in  1876. 
On  December  yth  of  that  year  a  bright  spot  was  seen 
upon  Saturn's  equator.  It  elongated  itself  from  day 
to  day,  and  remained  visible  for  several  weeks.  Such 
a  thing  had  never  before  been  known  upon  this 
planet,  and  had  it  not  been  that  Professor  Hall  was 
engaged  in  observations  upon  the  satellites,  it  would 
not  have  been  seen  then.  A  similar  spot  on  the  planet 
was  recorded  in  1902,  and  much  more  extensively 
noticed.  On  this  occasion  the  spot  appeared  in  a 
higher  latitude  from  the  planet's  equator  than  did 
Professor  Hall's.  At  this  appearance  the  time  of  the 
planet's  revolution  on  its  axis  was  found  to  be  some- 
what greater  than  in  1876,  in  accordance  with  the 
general  law  exhibited  in  the  rotations  of  the  sun  and 

96 


THE  GREAT  REFRACTOR    OF  THE   NATIONAL   OBSERVATORY  AT  WASHINGTON 


MAKING    AND    USING    A    TELESCOPE 

of  Jupiter.  Notwithstanding  their  transient  charac- 
ter, these  two  spots  have  afforded  the  only  determi- 
nation of  the  time  of  revolution  of  Saturn  which  has 
been  made  since  Herschel  the  elder. 

Of  the  satellites  of  Saturn  the  brightest  is  Titan, 
which  can  be  seen  with  the  smallest  telescope,  and 
revolves  around  the  planet  in  fifteen  days.  lapetus, 
the  outer  satellite,  is  remarkable  for  varying  greatly 
in  brilliancy  during  its  revolution  around  the  planet. 
Any  one  having  the  means  and  ability  to  make  ac- 
curate photometrical  estimates  of  the  light  of  this 
satellite  in  all  points  of  its  orbit,  can  thereby  render 
a  valuable  service  to  astronomy. 

The  observations  of  Venus,  by  which  the  astrono- 
mers of  the  last  century  supposed  themselves  to  have 
discovered  its  time  of  rotation  on  its  axis,  were  made 
with  telescopes  much  inferior  to  ours.  Although 
their  observations  have  not  been  confirmed,  some 
astronomers  are  still  inclined  to  think  that  their 
results  have  not  been  refuted  by  the  failure  of  recent 
observers  to  detect  those  changes  which  the  older 
ones  describe  on  the  surface  of  the  planet.  With  a 
six-inch  telescope  of  the  best  quality,  and  with  time 
to  choose  the  most  favorable  moment,  one  will  be  as 
well  equipped  to  settle  the  question  of  the  rotation 
of  Venus  as  the  best  observer.  The  few  days  near 
each  inferior  conjunction  are  especially  to  be  taken 
advantage  of. 

The  questions  to  be  settled  are  two :  first,  are  there 
any  dark  spots  or  other  markings  on  the  disk  ?  second, 
are  there  any  irregularities  in  the  form  of  the  sharp 
cusps?  The  central  portions  of  the  disk  are  much 
darker  than  the  outline,  and  it  is  probably  this  fact 
which  has  given  rise  to  the  impression  of  dark  spots. 

97 


SIDE-LIGHTS    ON    ASTRONOMY 

Unless  this  apparent  darkness  changes  from  time  to 
time,  or  shows  some  irregularity  in  its  outline,  it 
cannot  indicate  any  rotation  of  the  planet.  The 
best  time  to  scrutinize  the  sharp  cusps  will  be  when 
the  planet  is  nearly  on  the  line  from  the  earth  to 
the  sun.  The  best  hour  of  the  day  is  near  sunset, 
the  half -hour  following  sunset  being  the  best  of  all. 
But  if  Venus  is  near  the  sun,  she  will  after  sunset  be 
too  low  down  to  be  well  seen,  and  must  be  looked  at 
late  in  the  afternoon. 

The  planet  Mars  must  always  be  an  object  of 
great  interest,  because  of  all  the  heavenly  bodies  it 
is  that  which  appears  to  bear  the  greatest  resemblance 
to  the  earth.  It  comes  into  opposition  at  intervals 
of  a  little  more  than  two  years,  and  can  be  well  seen 
only  for  a  month  or  two  before  and  after  each  op- 
position. It  is  hopeless  to  look  for  the  satellites  of 
Mars  with  any  but  the  greatest  telescopes  of  the 
world.  But  the  markings  on  the  surface,  from  which 
the  time  of  rotation  has  been  determined,  and  which 
indicate  a  resemblance  to  the  surface  of  our  own 
planet,  can  be  well  seen  with  telescopes  of  six  inches 
aperture  and  upward.  One  or  both  of  the  bright 
polar  spots,  which  are  supposed  to  be  due  to  de- 
posits of  snow,  can  be  seen  with  smaller  telescopes 
when  the  situation  of  the  planet  is  favorable. 

The  case  is  different  with  the  so-called  canals  dis- 
covered by  Schiaparelli  in  1877,  which  have  ever 
since  excited  so  much  interest,  and  given  rise  to  so 
much  discussion  as  to  their  nature.  The  astronomer 
who  has  had  the  best  opportunities  for  studying 
them  is  Mr.  Percival  Lowell,  whose  observatory  at 
Flaggstaff,  Arizona,  is  finely  situated  for  the  purpose, 
while  he  also  has  one  of  the  best  if  not  the  largest 

98 


MAKING    AND    USING    A    TELESCOPE 

of  telescopes.  There  the  canals  are  seen  as  fine  dark 
lines;  but,  even  then,  they  must  be  fifty  miles  in 
breadth,  so  that  the  word  "canal"  may  be  regarded 
as  a  misnomer. 

Although  the  planet  Jupiter  does  not  present  such 
striking  features  as  Saturn,  it  is  of  even  more  interest 
to  the  amateur  astronomer,  because  he  can  study  it 
with  less  optical  power,  and  see  more  of  the  changes 
upon  its  surface.  Every  work  on  astronomy  tells 
in  a  general  way  of  the  belts  of  Jupiter,  and  many 
speculate  upon  their  causes.  The  reader  of  recent 
works  knows  that  Jupiter  is  supposed  to  be  not  a 
solid  mass  like  the  earth,  but  a  great  globe  of  molten 
and  vaporous  matter,  intermediate  in  constitution 
between  the  earth  and  the  sun.  The  outer  surfac 
which  we  see  is  probably  a  hot  mass  of  vapor  hun- 
dreds of  miles  deep,  thrown  up  from  the  heated  in- 
terior. The  belts  are  probably  cloudlike  forms  in 
this  vaporous  mass.  Certain  it  is  that  they  are 
continually  changing,  so  that  the  planet  seldom  looks 
exactly  the  same  on  two  successive  evenings.  The 
rotation  of  the  planet  can  be  very  well  seen  by  an 
hour's  watching.  In  two  hours  an  object  at  the 
centre  of  the  disk  will  move  off  to  near  the  margin. 

The  satellites  of  this  planet,  in  their  ever -vary- 
ing phases,  are  objects  of  perennial  interest.  Their 
eclipses  may  be  observed  with  a  very  small  telescope, 
if  one  knows  when  to  look  for  them.  To  do  this  suc- 
cessfully, and  without  waste  of  time,  it  is  necessary 
to  have  an  astronomical  ephemeris  for  the  year. 
All  the  observable  phenomena  are  there  predicted 
for  the  convenience  of  observers.  Perhaps  the  most 
curious  observation  to  be  made  is  that  of  the  shadow 
.of  the  satellite  crossing  the  disk  of  Jupiter.  The 

99 


SIDE-LIGHTS    ON    ASTRONOMY 

writer  has  seen  this  perfectly  with  a  six-inch  tele- 
scope, and  a  much  smaller  one  would  probably  show 
it  well.  With  a  telescope  of  this  size,  or  a  little 
larger,  the  satellites  can  be  seen  between  us  and 
Jupiter.  Sometimes  they  appear  a  little  brighter 
than  the  planet,  and  sometimes  a  little  fainter. 

Of  the  remaining  large  planets,  Mercury,  the  inner 
one,  and  Uranus  and  Neptune,  the  two  outer  ones, 
are  of  less  interest  than  the  others  to  an  amateur 
with  a  small  telescope,  because  they  are  more  diffi- 
cult to  see.  Mercury  can,  indeed,  be  observed  with 
the  smallest  instrument,  but  no  physical  configura- 
tions or  changes  have  ever  been  made  out  upon  his 
surface.  The  question  whether  any  such  can  be 
observed  is  still  an  open  one,  which  can  be  settled 
only  by  long  and  careful  scrutiny.  A  small  telescope 
is  almost  as  good  for  this  purpose  as  a  large  one,  be- 
cause the  atmospheric  difficulties  in  the  way  of  getting 
a  good  view  of  the  planet  cannot  be  lessened  by  an 
increase  of  telescopic  power. 

Uranus  and  Neptune  are  so  distant  that  telescopes 
of  considerable  size  and  high  magnifying  power  are 
necessary  to  show  their  disks.  In  small  telescopes 
they  have  the  appearance  of  stars,  and  the  observer 
has  no  way  of  distinguishing  them  from  the  sur- 
rounding stars  unless  he  can  command  the  best  as- 
tronomical appliances,  such  as  star  maps,  circles  on 
his  instrument,  etc.  It  is,  however,  to  be  remarked, 
as  a  fact  not  generally  known,  that  Uranus  can  be 
well  seen  with  the  naked  eye  if  one  knows  where  to 
look  for  it.  To  recognize  it,  it  is  necessary  to  have 
an  astronomical  ephemeris  showing  its  right  ascen- 
sion and  declination,  and  star  maps  showing  where 
the  parallels  of  right  ascension  and  declination  lie 

100 


MAKING    AND    USING    A    TELESCOPE 

among  the  stars.  When  once  found  by  the  naked 
eye,  there  will,  of  course,  be  no  difficulty  in  pointing 
the  telescope  upon  it. 

Of  celestial  objects  which  it  is  well  to  keep  a  watch 
upon,  and  which  can  be  seen  to  good  advantage  with 
inexpensive  instruments,  the  sun  may  be  considered 
as  holding  the  first  place.  Astronomers  who  make 
a  specialty  of  solar  physics  have,  especially  in  this 
country,  so  many  other  duties,  and  their  view  is  so 
often  interrupted  by  clouds,  that  a  continuous  record 
of  the  spots  on  the  sun  and  the  changes  they  under- 
go is  hardly  possible.  Perhaps  one  of  the  most  in- 
teresting and  useful  pieces  of  astronomical  work 
which  an  amateur  can  perform  will  consist  of  a  record 
of  the  origin  and  changes  of  form  of  the  solar  spots 
and  faculse.  What  does  a  spot  look  like  when  it  first 
comes  into  sight?  Does  it  immediately  burst  forth 
with  considerable  magnitude,  or  does  it  begin  as  the 
smallest  visible  speck,  and  gradually  grow?  When 
several  spots  coalesce  into  one,  how  do  they  do  it? 
When  a  spot  breaks  up  into  several  pieces,  what  is 
the  seeming  nature  of  the  process?  How  do  the 
groups  of  brilliant  points  called  faculse  come,  change, 
and  grow?  All  these  questions  must  no  doubt  be 
answered  in  various  ways,  according  to  the  behavior 
of  the  particular  spot,  but  the  record  is  rather  meagre, 
and  the  conscientious  and  industrious  amateur  will 
be  able  to  amuse  himself  by  adding  to  it,  and  possibly 
may  make  valuable  contributions  to  science  in  the 
same  way. 

Still  another  branch  of  astronomical  observation, 
in  which  industry  and  skill  count  for  more  than  ex- 
pensive instruments,  is  the  search  for  new  comets. 
This  requires  a  very  practised  eye,  in  order  that  the 

101 


SIDE-LIGHTS    ON    ASTRONOMY 

comet  may  be  caught  among  the  crowd  of  stars  which 
flit  across  the  field  of  view  as  the  telescope  is  moved. 
It  is  also  necessary  to  be  well  acquainted  with  a  num- 
ber of  nebulae  which  look  very  much  like  comets. 
The  search  can  be  made  with  almost  any  small 
telescope,  if  one  is  careful  to  use  a  very  low  power. 
With  a  four-inch  telescope  a  power  not  exceeding 
twenty  should  be  employed.  To  search  with  ease, 


THE    "  BROKEN-BACKED    COMET-SEEKER 


and  in  the  best  manner,  the  observer  should  have 
what  among  astronomers  is  familiarly  known  as  a 
"broken-backed  telescope."  This  instrument  has 
the  eye-piece  on  the  end  of  the  axis,  where  one  would 
never  think  of  looking  for  it.  By  turning  the  in- 
strument on  this  axis,  it  sweeps  from  one  horizon 
through  the  zenith  and  over  to  the  other  horizon 
without  the  observer  having  to  move  his  head.  This 
is  effected  by  having  a  reflector  in  the  central  part 

102 


MAKING    AND    USING    A    TELESCOPE 

of  the  instrument,  which  throws  the  rays  of  light  at 
right  angles  through  the  axis. 

How  well  this  search  can  be  conducted  by  ob- 
servers with  limited  means  at  their  disposal  is  shown 
by  the  success  of  several  American  observers,  among 
whom  Messrs.  W.  R.  Brooks,  E.  E.  Barnard,  and  Lewis 
Swift  are  well  known.  The  cometary  discoveries  of 
these  men  afford  an  excellent  illustration  of  how  much 
can  be  done  with  the  smallest  means  when  one  sets  to 
work  in  the  right  spirit. 

The  larger  number  of  wonderful  telescopic  objects 
are  to  be  sought  for  far  beyond  the  confines  of  the 
solar  system,  in  regions  from  which  light  requires 
years  to  reach  us.  On  account  of  their  great  dis- 
tance, these  objects  generally  require  the  most 
powerful  telescopes  to  be  seen  in  the  best  manner; 
but  there  are  quite  a  number  within  the  range  of  the 
amateur.  Looking  at  the  Milky  Way,  especially  its 
southern  part,  on  a  clear  winter  or  summer  evening, 
tufts  of  light  will  be  seen  here  and  there.  On  examin- 
ing these  tufts  with  a  telescope,  they  will  be  found 
to  consist  of  congeries  of  stars.  Many  of  these  groups 
are  of  the  greatest  beauty,  with  only  a  moderate 
optical  power.  Of  all  the  groups  in  the  Milky  Way 
the  best  known  is  that  in  the  sword-handle  of  Perseus, 
which  may  be  seen  during  the  greater  part  of  the 
year,  and  is  distinctly  visible  to  the  naked  eye  as  a 
patch  of  diffused  light.  With  the  telescope  there  are 
seen  in  this  patch  two  closely  connected  clusters  of 
stars,  or  perhaps  we  ought  rather  to  say  two  centres 
of  condensation. 

Another  object  of  the  same  class  is  Pr&sepe  in  the 
constellation  Cancer.  This  can  be  very  distinctly 
seen  by  the  naked  eye  on  a  clear  moonless  night  in 
s  103 


SIDE-LIGHTS    ON    ASTRONOMY 

winter  or  spring  as  a  faint  nebulous  object,  surrounded 
by  three  small  stars.  The  smallest  telescope  shows 
it  as  a  group  of  stars. 

Of  all  stellar  objects,  the  great  nebula  of  Orion  is 
that  which  has  most  fascinated  the  astronomers  of 
two  centuries.  It  is  distinctly  visible  to  the  naked 
eye,  and  may  be  found  without  difficulty  on  any  win- 
ter night.  The  three  bright  stars  forming  the  sword- 
belt  of  Orion  are  known  to  every  one  who  has  noticed 
that  constellation.  Below  this  belt  is  seen  another 
triplet  of  stars,  not  so  bright,  and  lying  in  a  north 
and  south  direction.  The  middle  star  of  this  triplet 
is  the  great  nebula.  At  first  the  naked  eye  sees  noth- 
ing to  distinguish  it  from  other  stars,  but  if  closely 
scanned  it  will  be  seen  to  have  a  hazy  aspect.  A 
four-inch  telescope  will  show  its  curious  form.  Not 
the  least  interesting  of  its  features  are  the  four 
stars  known  as  the  "Trapezium,"  which  are  lo- 
cated in  a  dark  region  near  its  centre.  In  fact,  the 
whole  nebula  is  dotted  with  stars,  which  add  great- 
ly to  the  effect  produced  by  its  mysterious  as- 
pect. 

The  great  nebula  of  Andromeda  is  second  only  to 
that  of  Orion  in  interest.  Like  the  former,  it  is  dis- 
tinctly visible  to  the  naked  eye,  having  the  aspect 
of  a  faint  comet.  The  most  curious  feature  of  this 
object  is  that  although  the  most  powerful  telescopes 
do  not  resolve  it  into  stars,  it  appears  in  the  spectro- 
scope as  if  it  were  solid  matter  shining  by  its  own 
light. 

The  above  are  merely  selections  from  the  countless 
number  of  objects  which  the  heavens  offer  to  tele- 
scopic study.  Many  such  are  described  in  astronom- 
ical works,  but  the  amateur  can  gratify  his  curiosity 

104 


NEBULA    IN    ORION 


MAKING    AND    USING    A    TELESCOPE 

to  almost  any  extent  by  searching  them  out  for  him- 
self. 

Ever  since  1878  a  red  spot,  unlike  any  before 
noticed,  has  generally  been  visible  on  Jupiter.  At 
first  it  was  for  several  years  a  very  conspicuous  ob- 
ject, but  gradually  faded  away,  so  that  since  1890 
it  has  been  made  out  only  with  difficulty.  But  it 
is  now  regarded  as  a  permanent  feature  of  the  planet. 
There  is  some  reason  to  believe  it  was  occasionally 
seen  long  before  attention  was  first  attracted  to  it. 
Doubtless,  when  it  can  be  seen  at  all,  practice  in  ob- 
serving such  objects  is  more  important  than  size  of 
telescope. 


VI 

WHAT   THE    ASTRONOMERS    ARE    DOING 

IN  no  field  of  science  has  human  knowledge  been 
more  extended  in  our  time  than  in  that  of  astron- 
omy. Forty  years  ago  astronomical  research  seemed 
quite  barren  of  results  of  great  interest  or  value  to 
our  race.  The  observers  of  the  world  were  working 
on  a  traditional  system,  grinding  out  results  in  an 
endless  course,  without  seeing  any  prospect  of  the 
great  generalizations  to  which  they  might  ultimately 
lead.  Now  this  is  all  changed.  A  new  instrument, 
the  spectroscope,  has  been  developed,  the  extent  of 
whose  revelations  we  are  just  beginning  to  learn^ 
although  it  has  been  more  than  thirty  years  in  use. 
The  application  of  photography  has  been  so  ex- 
tended that,  in  some  important  branches  of  astro- 
nomical work,  the  observer  simply  photographs  the 
phenomenon  which  he  is  to  study,  and  then  makes 
his  observation  on  the  developed  negative. 

The  world  of  astronomy  is  one  of  the  busiest  that 
can  be  found  to-day,  and  the  writer  proposes,  with 
the  reader's  courteous  consent,  to  take  him  on  a  stroll 
through  it  and  see  what  is  going  on.  We  may  be- 
gin our  inspection  with  a  body  which  is,  for  us,  next 
to  the  earth,  the  most  important  in  the  universe.  I 
mean  the  sun.  At  the  Greenwich  Observatory  the 
sun  has  for  more  than  twenty  years  been  regularly 

106 


WHAT   THE   ASTRONOMERS   ARE    DOING 

photographed  on  every  clear  day,  with  the  view  of 
determining  the  changes  going  on  in  its  spots.  In 
recent  years  these  observations  have  been  supple- 
mented by  others,  made  at  stations  in  India  and 
Mauritius,  so  that  by  the  combination  of  all  it  is 
quite  exceptional  to  have  an  entire  day  pass  without 
at  least  one  photograph  being  taken.  On  these  ob- 
servations must  mainly  rest  our  knowledge  of  the 
curious  cycle  of  change  in  the  solar  spots,  which  goes 
through  a  period  of  about  eleven  years,  but  of  which 
no  one  has  as  yet  been  able  to  establish  the  cause. 

This  Greenwich  system  has  been  extended  and  im- 
proved by  an  American.  Professor  George  E.  Hale, 
formerly  Director  of  the  Yerkes  Observatory,  has  de- 
vised an  instrument  for  taking  photographs  of  the 
sun  by  a  single  ray  of  the  spectrum.  The  light  emit- 
ted by  calcium,  the  base  of  lime,  and  one  of  the  sub- 
stances most  abundant  in  the  sun,  is  often  selected 
to  impress  the  plate. 

The  Carnegie  Institution  has  recently  organized 
an  enterprise  for  carrying  on  the  study  of  the  sun 
under  a  combination  of  better  conditions  than  were 
ever  before  enjoyed.  The  first  requirement  in  such 
a  case  is  the  ablest  and  most  enthusiastic  worker  in 
the  field,  ready  to  devote  all  his  energies  to  its  cul- 
tivation. This  requirement  is  found  in  the  person 
of  Professor  Hale  himself.  The  next  requirement  is 
an  atmosphere  of  the  greatest  transparency,  and  a 
situation  at  a  high  elevation  above  sea-level,  so  that 
the  passage  of  light  from  the  sun  to  the  observer 
shall  be  obstructed  as  little  as  possible  by  the  mists 
and  vapors  near  the  earth's  surface.  This  require- 
ment is  reached  by  placing  the  observatory  on  Mount 
Wilson,  near  Pasadena,  California,  where  the  cli- 

107 


SIDE-LIGHTS    ON    ASTRONOMY 

mate  is  found  to  be  the  best  of  any  in  the  United 
States,  and  probably  not  exceeded  by  that  of  any 
other  attainable  point  in  the  world.  The  third  re- 
quirement is  the  best  of  instruments,  specially  devised 
to  meet  the  requirements.  In  this  respect  we  may 
be  sure  that  nothing  attainable  by  human  ingenuity 
will  be  found  wanting. 

Thus  provided,  Professor  Hale  has  entered  upon 
the  task  of  studying  the  sun,  and  recording  from  day 
to  day  all  the  changes  going  on  in  it,  using  specially 
devised  instruments  for  each  purpose  in  view.  Pho- 
tography is  made  use  of  through  almost  the  entire 
investigation.  A  full  description  of  the  work  would 
require  an  enumeration  of  technical  details,  into 
which  we  need  not  enter  at  present.  Let  it,  there- 
fore, suffice  to  say  in  a  general  way  that  the  study 
of  the  sun  is  being  carried  on  on  a  scale,  and  with  an 
energy  worthy  of  the  most  important  subject  that 
presents  itself  to  the  astronomer.  Closely  associated 
with  this  work  is  that  of  Professor  Langley  and  Dr. 
Abbot,  at  the  Astro  -  Physical  Observatory  of  the 
Smithsonian  Institution,  who  have  recently  com- 
pleted one  of  the  most  important  works  ever  carried 
out  on  the  light  of  the  sun.  They  have  for  years 
been  analyzing  those  of  its  rays  which,  although  en- 
tirely invisible  to  our  eyes,  are  of  the  same  nature 
as  those  of  light,  and  are  felt  by  us  as  heat.  To  do 
this,  Langley  invented  a  sort  of  artificial  eye,  which 
he  called  a  bolometer,  in  which  the  optic  nerve  is 
made  of  an  extremely  thin  strip  of  metal,  so  slight 
that  one  can  hardly  see  it,  which  is  traversed  by  an 
electric  current.  This  eye  would  be  so  dazzled  by 
the  heat  radiated  from  one's  body  that,  when  in  use, 
it  must  be  protected  from  all  such  heat  by  being  en- 

108 


WHAT   THE    ASTRONOMERS   ARE    DOING 

closed  in  a  case  kept  at  a  constant  temperature  by 
being  immersed  in  water.  With  this  eye  the  two  ob- 
servers have  mapped  the  heat  rays  of  the  sun  down 
to  an  extent  and  with  a  precision  which  were  before 
entirely  unknown. 

The  question  of  possible  changes  in  the  sun's  radia- 
tion, and  of  the  relation  of  those  changes  to  human 
welfare,  still  eludes  our  scrutiny.  With  all  the  ef- 
forts that  have  been  made,  the  physicist  of  to-day 
has  not  yet  been  able  to  make  anything  like  an  exact 
determination  of  the  total  amount  of  heat  received 
from  the  sun.  The  largest  measurements  are  almost 
double  the  smallest.  This  is  partly  due  to  the  at-" 
mosphere  absorbing  an  unknown  and  variable  frac- 
tion of  the  sun's  rays  which  pass  through  it,  and 
partly  to  the  difficulty  of  distinguishing  the  heat 
radiated  by  the  sun  from  that  radiated  by  terrestrial 
objects. 

In  one  recent  instance,  a  change  in  the  sun's  radia- 
tion has  been  noticed  in  various  parts  of  the  world, 
and  is  of  especial  interest  because  there  seems  to  be 
little  doubt  as  to  its  origin.  In  the  latter  part  of 
1902  an  extraordinary  diminution  was  found  in  the 
intensity  of  the  sun's  heat,  as  measured  by  the  bolom- 
eter and  other  instruments.  This  continued  through 
the  first  part  of  1903,  with  wide  variations  at  differ- 
ent places,  and  it  was  more  than  a  year  after  the 
first  diminution  before  the  sun's  rays  again  assumed 
their  ordinary  intensity. 

This  result  is  now  attributed  to  the  eruption  of 
Mount  Pelee,  during  which  an  enormous  mass  of 
volcanic  dust  and  vapor  was  projected  into  the 
higher  regions  of  the  air,  and  gradually  carried  over 
the  entire  earth  by  winds  and  currents.  Many  of  our 

109 


SIDE-LIGHTS    ON    ASTRONOMY 

readers  may  remember  that  something  yet  more 
striking  occurred  after  the  great  cataclasm  at  Kra- 
katoa  in  1883,  when,  for  more  than  a  year,  red  sun- 
sets and  red  twilights  of  a  depth  of  shade  never  be- 
fore observed  were  seen  in  every  part  of  the  world. 

What  we  call  universology — the  knowledge  of  the 
structure  and  extent  of  the  universe  —  must  begin 
with  a  study  of  the  starry  heavens  as  we  see  them. 
There  are  perhaps  one  hundred  million  stars  in  the 
sky  within  the  reach  of  telescopic  vision.  This  num- 
ber is  too  great  to  allow  of  all  the  stars  being  studied 
individually ;  yet,  to  form  the  basis  for  any  conclusion, 
we  must  know  the  positions  and  arrangement  of  as 
many  of  them  as  we  can  determine. 

To  do  this  the  first  want  is  a  catalogue  giving  very 
precise  positions  of  as  many  of  the  brighter  stars  as 
possible.  The  principal  national  observatories,  as 
well  as  some  others,  are  engaged  in  supplying  this 
want.  Up  to  the  present  time  about  200,000  stars 
visible  in  our  latitudes  have  been  catalogued  on  this 
precise  plan,  and  the  work  is  still  going  on.  In  that 
part  of  the  sky  which  we  never  see,  because  it  is 
only  visible  from  the  southern  hemisphere,  the  corre- 
sponding work  is  far  from  being  as  extensive.  Sir 
David  Gill,  astronomer  at  the  Cape  of  Good  Hope, 
and  also  the  directors  of  other  southern  observa- 
tories, are  engaged  in  pushing  it  forward  as  rapidly 
as  the  limited  facilities  at  their  disposal  will  allow. 

Next  in  order  comes  the  work  of  simply  listing  as 
many  stars  as  possible.  Here  the  most  exact  posi- 
tions are  not  required.  It  is  only  necessary  to  lay 
down  the  position  of  each  star  with  sufficient  exact- 
ness to  distinguish  it  from  all  its  neighbors.  About 
400,000  stars  were  during  the  last  half -century  listed 

no 


WHAT  THE  ASTRONOMERS  ARE  DOING 

in  this  way  at  the  observatory  of  Bonn  by  Argelander, 
Schonfeld,  and  their  assistants.  This  work  is  now 
being  carried  through  the  southern  hemisphere  on  a 
large  scale  by  Thome,  Director  of  the  Cordoba  Ob- 
servatory, in  the  Argentine  Republic.  This  was 
founded  thirty  years  ago  by  our  Dr.  B.  A.  Gould, 
who  turned  it  over  to  Dr.  Thome  in  1886.  The  latter 
has,  up  to  the  present  time,  fixed  and  published  the 
positions  of  nearly  half  a  million  stars.  This  work  of 
Thome  extends  to  fainter  stars  than  any  other  yet 
attempted,  so  that,  as  it  goes  on,  we  have  more  stars 
listed  in  a  region  invisible  in  middle  northern  lati- 
tudes than  we  have  for  that  part  of  the  sky  we  can 
see.  Up  to  the  present  time  three  quarto  volumes 
giving  the  positions  and  magnitudes  of  the  stars  have 
appeared.  Two  or  three  volumes  more,  and,  per- 
haps, ten  or  fifteen  years,  will  be  required  to  com- 
plete the  work. 

About  twenty  years  ago  it  was  discovered  that,  by 
means  of  a  telescope  especially  adapted  to  this  pur- 
pose, it  was  possible  to  photograph  many  more  stars 
than  an  instrument  of  the  same  size  would  show  to 
the  eye.  This  discovery  was  soon  applied  in  various 
quarters.  Sir  David  Gill,  with  characteristic  energy, 
photographed  the  stars  of  the  southern  sky  to  the 
number  of  nearly  half  a  million.  As  it  was  beyond 
his  power  to  measure  off  and  compute  the  positions 
of  the  stars  from  his  plates,  the  latter  were  sent  to 
Professor  J.  C.  Kapteyn,  of  Holland,  who  undertook 
the  enormous  labor  of  collecting  them  into  a  cata- 
logue, the  last  volume  of  which  was  published  in 
1899.  One  curious  result  of  this  enterprise  is  that 
the  work  of  listing  the  stars  is  more  complete  for 
the  southern  hemisphere  than  for  the  northern. 

in 


SIDE-LIGHTS    ON    ASTRONOMY 

Another  great  photographic  work  now  in  progress 
has  to  do  with  the  millions  of  stars  which  it  is  im- 
possible to  handle  individually.  Fifteen  years  ago 
an  association  of  observatories  in  both  hemispheres 
undertook  to  make  a  photographic  chart  of  the  sky 
on  the  largest  scale.  Some  portions  of  this  work  are 
now  approaching  completion,  but  in  others  it  is  still 
in  a  backward  state,  owing  to  the  failure  of  several 
South  American  observatories  to  carry  out  their 
part  of  the  programme.  When  it  is  all  done  we  shall 
have  a  picture  of  the  sky,  the  study  of  which  may 
require  the  labor  of  a  whole  generation  of  astronomers. 

Quite  independently  of  this  work,  the  Harvard 
University,  under  the  direction  of  Professor  Picker- 
ing, keeps  up  the  work  of  photographing  the  sky  on 
a  surprising  scale.  On  this  plan  we  do  not  have  to 
leave  it  to  posterity  to  learn  whether  there  is  any 
change  in  the  heavens,  for  one  result  of  the  enter- 
prise has  been  the  discovery  of  thirteen  of  the  new 
stars  which  now  and  then  blaze  out  in  the  heavens 
at  points  where  none  were  before  known.  Professor 
Pickering's  work  has  been  continually  enlarged  and 
improved  until  about  150,000  photographic  plates, 
showing  from  time  to  time  the  places  of  countless 
millions  of  stars  among  their  fellows  are  now  stored 
at  the  Harvard  Observatory.  Not  less  remarkable 
than  this  wealth  of  material  has  been  the  develop- 
ment of  skill  in  working  it  up.  Some  idea  of  the 
work  will  be  obtained  by  reflecting  that,  thirty  years 
ago,  careful  study  of  the  heavens  by  astronomers 
devoting  their  lives  to  the  task  had  resulted  in  the 
discovery  of  some  two  or  three  hundred  stars,  vary- 
ing in  their  light.  Now,  at  Harvard,  through  keen 
eyes  studying  and  comparing  successive  photographs 

112 


WHAT  THE  ASTRONOMERS  ARE   DOING 

not  only  of  isolated  stars,  but  of  clusters  and  agglom- 
erations of  stars  in  the  Milky  Way  and  elsewhere, 
discoveries  of  such  objects  numbering  hundreds  have 
been  made,  and  the  work  is  going  on  with  ever-in- 
creasing speed.  Indeed,  the  number  of  variable 
stars  now  known  is  such  that  their  study  as  in- 
dividual objects  no  longer  suffices,  and  they  must 
hereafter  be  treated  statistically  with  reference  to 
their  distribution  in  space,  and  their  relations  to 
one  another,  as  a  census  classifies  the  entire  popula- 
tion without  taking  any  account  of  individuals. 

The  works  just  mentioned  are  concerned  with  the 
stars.  But  the  heavenly  spaces  contain  nebulas  as 
well  as  stars ;  and  photography  can  now  be  even  more 
successful  in  picturing  them  than  the  stars.  A  few 
years  ago  the  late  lamented  Keeler,  at  the  Lick 
Observatory,  undertook  to  see  what  could  be  done 
by  pointing  the  Crossley  reflecting  telescope  at  the 
sky  and  putting  a  sensitive  photographic  plate  in 
the  focus.  He  was  surprised  to  find  that  a  great 
number  of  nebulae,  the  existence  of  which  had  never 
before  been  suspected,  were  impressed  on  the  plate. 
Up  to  the  present  time  the  positions  of  about  8000 
of  these  objects  have  been  listed.  Keeler  found  that 
there  were  probably  200,000  nebulas  in  the  heavens 
capable  of  being  photographed  with  the  Crossley  re- 
flector. But  the  work  of  taking  these  photographs 
is  so  great,  and  the  number  of  reflecting  telescopes 
which  can  be  applied  to  it  so  small,  that  no  one  has 
ventured  to  seriously  commence  it.  It  is  worthy  of 
remark  that  only  a  very  small  fraction  of  these  ob- 
jects which  can  be  photographed  are  visible  to  the 
eye,  even  with  the  most  powerful  telescope. 

This  demonstration  of  what  the  reflecting  telescope 


SIDE-LIGHTS    ON    ASTRONOMY 

can  do  may  be  regarded  as  one  of  the  most  impor- 
tant discoveries  of  our  time  as  to  the  capabilities  of 
astronomical  instruments.     It  has  long  been  known  ] 
that  the  image  formed  in  the  focus  of  the  best  re- 
fracting telescope  is  affected  by  an  imperfection  aris- 
ing from  the  different  action  of  the  glasses  on  rays   \ 
of  light  of  different  colors.     Hence,  the  image  of  a 
star  can  never  be  seen  or  photographed  with  such  I 
an  instrument,  as  an  actual  point,  but  only  as  a    ' 
small,  diffused  mass.     This  difficulty  is  avoided  in 
the  reflecting  telescope;  but  a  new  difficulty  is  found   } 
in  the  bending  of  the  mirror  under  the  influence  of 
its  own  weight.     Devices  for  overcoming  this  had    \ 
been  so  far  from  successful  that,  when  Mr.  Crossley   j 
presented  his  instrument  to  the  Lick  Observatory, 
it  was  feared  that  little  of  importance  could  be  done  I 
with  it.     But   as   often   happens   in   human   affairs 
outside  the  field  of  astronomy,  when  ingenious  and  I 
able  men  devote  their  attention  to  the  careful  study 
of  a  problem,  it  was  found  that  new  results  could  be 
reached.     Thus  it  was  that,   before  a  great  while,   J 
what   was   supposed   to   be   an   inferior   instrument 
proved  not  only  to  have  qualities  not  before  suspected, 
but  to  be  the  means  of  making  an  important  addition  j 
to  the  methods  of  astronomical  investigation. 

In  order  that  our  knowledge  of  the  position  of  a 
star  may  be  complete,  we  must  know  its  distance. 
This  can  be  measured  only  through  the  star's  paral- 
lax— that  is  to  say,  the  slight  change  in  its  direction 
produced  by  the  swing  of  our  earth  around  its  orbit. 
But  so  vast  is  the  distance  in  question  that  this 
change  is  immeasurably  small,  except  for,  perhaps,  a 
few  hundred  stars,  and  even  for  these  few  its  meas- 
urement almost  baffles  the  skill  of  the  most  expert 

114 


WHAT    THE    ASTRONOMERS    ARE    DOING 

astronomer.  Progress  in  this  direction  is  therefore 
very  slow,  and  there  are  probably  not  yet  a  hundred 
stars  of  which  the  parallax  has  been  ascertained  with 
any  approach  to  certainty.  Dr.  Chase  is  now  com- 
pleting an  important  work  of  this  kind  at  the  Yale 
Observatory. 

To  the  most  refined  telescopic  observations,  as 
well  as  to  the  naked  eye,  the  stars  seem  all  alike, 
except  that  they  differ  greatly  in  brightness,  and 
somewhat  in  color.  But  when  their  light  is  analyzed 
by  the  spectroscope,  it  is  found  that  scarcely  any 
two  are  exactly  alike.  An  important  part  of  the 
work  of  the  astro-physical  observatories,  especially 
that  of  Harvard,  consists  in  photographing  the 
spectra  of  thousands  of  stars,  and  studying  the 
peculiarities  thus  brought  out.  At  Harvard  a  large 
portion  of  this  work  is  done  as  part  of  the  work  of 
the  Henry  Draper  Memorial,  established  by  his  widow 
in  memory  of  the  eminent  investigator  of  New  York, 
who  died  twenty  years  ago. 

By  a  comparison  of  the  spectra  of  stars  Sir  William 
Huggins  has  developed  the  idea  that  these  bodies, 
like  human  beings,  have  a  life  history.  They  are 
nebulas  in  infancy,  while  the  progress  to  old  age  is 
marked  by  a  constant  increase  in  the  density  of  their 
substance.  Their  temperature  also  changes  in  a  way 
analogous  to  the  vigor  of  the  human  being.  During 
a  certain  time  the  star  continually  grows  hotter  and 
hotter.  But  an  end  to  this  must  come,  and  it  cools 
off  in  old  age.  What  the  age  of  a  star  may  be  is 
hard  even  to  guess.  It  is  many  millions  of  years,  per- 
haps  hundreds,  possibly  even  thousands,  of  millions. 

Some  attempt  at  giving  the  magnitude  is  included 
in  every  considerable  list  of  stars.  The  work  of  de- 

a 


SIDE-LIGHTS    ON    ASTRONOMY 

termining  the  magnitudes  with  the  greatest  precision 
is  so  laborious  that  it  must  go  on  rather  slowly.  It 
is  being  pursued  on  a  large  scale  at  the  Harvard  Ob- 
servatory, as  well  as  in  that  of  Potsdam,  Germany. 

We  come  now  to  the  question  of  changes  in  the 
appearance  of  bright  stars.  It  seems  pretty  certain 
that  more  than  one  per  cent,  of  these  bodies  fluctuate 
to  a  greater  or  less  extent  in  their  light.  Observa- 
tions of  these  fluctuations,  in  the  case  of  at  least  the 
brighter  stars,  may  be  carried  on  without  any  instru- 
ment more  expensive  than  a  good  opera -glass — in 
fact,  in  the  case  of  stars  visible  to  the  naked  eye,  with 
no  instrument  at  all. 

As  a  general  rule,  the  light  of  these  stars  goes 
through  its  changes  in  a  regular  period,  which  is 
sometimes  as  short  as  a  few  hours,  but  generally 
several  days,  frequently  a  large  fraction  of  a  year 
or  even  eighteen  months.  Observations  of  these 
stars  are  made  to  determine  the  length  of  the  period 
and  the  law  of  variation  of  the  brightness.  Any 
person  with  a  good  eye  and  skill  in  making  estimates 
can  make  the  observations  if  he  will  devote  sufficient 
pains  to  training  himself;  but  they, require  a  degree 
of  care  and  assiduity  which  is  not  to  be  expected  of 
any  one  but  an  enthusiast  on  the  subject.  One  of 
the  most  successful  observers  of  the  present  time  is 
Mr.  W.  A.  Roberts,  a  resident  of  South  Africa,  whom 
the  Boer  war  did  not  prevent  from  keeping  up  a 
watch  of  the  southern  sky,  which  has  resulted  in 
greatly  increasing  our  knowledge  of  variable  stars. 
There  are  also  quite  a  number  of  astronomers  in 
Europe  and  America  who  make  this  particular  study 
their  specialty. 

During  the  past  fifteen  years  the  art  of  measuring 

116 


WHAT  THE  ASTRONOMERS  ARE  DOING 

the  speed  with  which  a  star  is  approaching  us  or  re- 
ceding from  us  has  been  brought  to  a  wonderful  de- 
gree of  perfection.  The  instrument  with  which  this 
was  first  done  was  the  spectroscope ;  it  is  now  replaced 
with  another  of  the  same  general  kind,  called  the 
spectrograph.  The  latter  differs  from  the  other  only 
in  that  the  spectrum  of  the  star  is  photographed,  and 
the  observer  makes  his  measures  on  the  negative. 
This  method  was  first  extensively  applied  at  the  Pots- 
dam Observatory  in  Germany,  and  has  lately  become 
one  of  the  specialties  of  the  Lick  Observatory,  where 
Professor  Campbell  has  brought  it  to  its  present  de- 
gree of  perfection.  The  Yerkes  Observatory  is  also 
beginning  work  in  the  same  line,  where  Professor 
Frost  is  already  rivalling  the  Lick  Observatory  in  the 
precision  of  his  measures. 

Let  us  now  go  back  to  our  own  little  colony  and 
see  what  is  being  done  to  advance  our  knowledge 
of  the  solar  system.  This  consists  of  planets,  on  one 
of  which  we  dwell,  moons  revolving  around  them, 
comets,  and  meteoric  bodies.  The  principal  national 
observatories  keep  up  a  more  or  less  orderly  system 
of  observations  of  the  positions  of  the  planets  and 
their  satellited  in  order  to  determine  the  laws  of  their 
motion.  As  in  the  case  of  the  stars,  it  is  necessary  to 
continue  these  observations  through  long  periods  of 
time  in  order  that  everything  possible  to  learn  may 
be  discovered. 

Our  own  moon  is  one  of  the  enigmas  of  the  mathe- 
matical astronomer.  Observations  show  that  she  is 
deviating  from  her  predicted  place,  and  that  this 
deviation  continues  to  increase.  True,  it  is  not  very 
great  when  measured  by  an  ordinary  standard.  The 
time  at  which  the  moon's  shadow  passed  a  given  point 

117 


SIDE-LIGHTS    ON    ASTRONOMY 

near  Norfolk  during  the  total  eclipse  of  May  29,  1900, 
was  only  about  seven  seconds  different  from  the  time 
given  in  the  Astronomical  Ephemeris.  The  path  of 
the  shadow  along  the  earth  was  not  out  of  place  by 
more  than  one  or  two  miles.  But,  small  though  these 
deviations  are,  they  show  that  something  is  wrong, 
and  no  one  has  as  yet  found  out  what  it  is.  Worse 
yet,  the  deviation  is  increasing  rapidly.  The  observ- 
ers of  the  total  eclipse  in  August,  1905,  were  surprised 
to  find  that  it  began  twenty  seconds  before  the  pre- 
dicted time.  The  mathematical  problems  involved 
in  correcting  this  error  are  of  such  complexity  that 
it  is  only  now  and  then  that  a  mathematician  turns 
up  anywhere  in  the  world  who  is  both  able  and  bold 
enough  to  attack  them. 

There  now  seems  little  doubt  that  Jupiter  is  a 
miniature  sun,  only  not  hot  enough  at  its  surface  to 
shine  by  its  own  light.  The  point  in  which  it  most 
resembles  the  sun  is  that  its  equatorial  regions  rotate 
in  less  time  than  do  the  regions  near  the  poles.  This 
shows  that  what  we  see  is  not  a  solid  body.  But 
none  of  the  careful  observers  have  yet  succeeded  in 
determining  the  law  of  this  difference  of  rotation. 

Twelve  years  ago  a  suspicion  which  had  long  been 
entertained  that  the  earth's  axis  of  rotation  varied 
a  little  from  time  to  time  was  verified  by  Chandler. 
The  result  of  this  is  a  slight  change  in  the  latitude  of 
all  places  on  the  earth's  surface,  which  admits  of  being 
determined  by  precise  observations.  The  National 
Geodetic  Association  has  established  four  observa- 
tories on  the  same  parallel  of  latitude — one  at  Gaith- 
ersburg,  Maryland,  another  on  the  Pacific  coast,  a 
third  in  Japan,  and  a  fourth  in  Italy — to  study  these 
variations  by  continuous  observations  from  night  to 

118 


WHAT  THE  ASTRONOMERS  ARE  DOING 

night.     This  work  is  now  going  forward  on  a  well- 
devised  plan. 

A  fact  which  will  appeal  to  our  readers  on  this  side 
of  the  Atlantic  is  the  success  of  American  astronomers. 
Sixty  years  ago  it  could  not  be  said  that  there  was  a 
well-known  observatory  on  the  American  continent. 
The  cultivation  of  astronomy  was  confined  to  a  pro- 
fessor here  and  there,  who  seldom  had  anything  bet- 
ter than  a  little  telescope  with  which  he  showed  the 
heavenly  bodies  to  his  students.  But  during  the 
past  thirty  years  all  this  has  been  changed.  The 
total  quantity  of  published  research  is  still  less  among 
us  than  on  the  continent  of  Europe,  but  the  number 
of  men  who  have  reached  the  highest  success  among 
us  may  be  judged  by  one  fact.  The  Royal  Astro- 
nomical Society  of  England  awards  an  annual  medal 
to  the  English  or  foreign  astronomer  deemed  most 
worthy  of  it.  The  number  of  these  medals  awarded 
to  Americans  within  twenty-five  years  is  about  equal 
to  the  number  awarded  to  the  astronomers  of  all 
other  nations  foreign  to  the  English.  That  this  pre- 
ponderance is  not  growing  less  is  shown  by  the  award 
of  medals  to  Americans  in  three  consecutive  years — 
1904,  1905,  and  1906.  The  recipients  were  Hale, 
Boss,  and  Campbell.  Of  the  fifty  foreign  associates 
chosen  by  this  society  for  their  eminence  in  astro- 
nomical research,  no  less  than  eighteen — more  than 
one-third — are  Americans. 


S' 


VII 

LIFE    IN   THE   UNIVERSE 

10  far  as  we  can  judge  from  what  we  see  on  our 
globe,  the  production  of  life  is  one  of  the  great- 
est and  most  incessant  purposes  of  nature.  Life  is 
absent  only  in  regions  of  perpetual  frost,  where  it 
never  has  an  opportunity  to  begin;  in  places  where 
the  temperature  is  near  the  boiling-point,  which  is 
found  to  be  destructive  to  it ;  and  beneath  the  earth's 
surface,  where  none  of  the  changes  essential  to  it  can 
come  about.  Within  the  limits  imposed  by  these 
prohibitory  conditions  —  that  is  to  say,  within  the 
range  of  temperature  at  which  water  retains  its  liquid 
state,  and  in  regions  where  the  sun's  rays  can  pene- 
trate and  where  wind  can  blow  and  water  exist  in  a 
liquid  form — life  is  the  universal  rule.  How  prodigal 
nature  seems  to  be  in  its  production  is  too  trite  a 
fact  to  be  dwelt  upon.  We  have  all  read  of  the 
millions  of  germs  which  are  destroyed  for  every  one 
that  comes  to  maturity.  Even  the  higher  forms  of 
life  are  found  almost  everywhere.  Only  small  islands 
have  ever  been  discovered  which  were  uninhabited, 
and  animals  of  a  higher  grade  are  as  widely  diffused 
as  man. 

If  it  would  be  going  too  far  to  claim  that  all  con- 
ditions may  have  forms  of  life  appropriate  to  them, 
it  would  be  going  as  much  too  far  in  the  other  direc- 

120 


LIFE    IN    THE    UNIVERSE 

tion  to  claim  that  life  can  exist  only  with  the  precise 
surroundings  which  nurture  it  on  this  planet.  It  is 
very  remarkable  in  this  connection  that  while  in  one 
direction  we  see  life  coming  to  an  end,  in  the  other 
direction  we  see  it  flourishing  more  and  more  up  to 
the  limit.  These  two  directions  are  those  of  heat  and 
cold.  We  cannot  suppose  that  life  would  develop  in 
any  important  degree  in  a  region  of  perpetual  frost, 
such  as  the  polar  regions  of  our  globe.  But  we  do 
not  find  any  end  to  it  as  the  climate  becomes  warmer. 
On  the  contrary,  every  one  knows  that  the  tropics 
are  the  most  fertile  regions  of  the  globe  in  its  pro- 
duction. The  luxuriance  of  the  vegetation  and  the 
number  of  the  animals  continually  increase  the  more 
tropical  the  climate  becomes.  Where  the  limit  may 
be  set  no  one  can  say.  But  it  would  doubtless  be 
far  above  the  present  temperature  of  the  equatorial 
regions. 

It  has  often  been  said  that  this  does  not  apply  to 
the  human  race,  that  men  lack  vigor  in  the  tropics. 
But  human  vigor  depends  on  so  many  conditions, 
hereditary  and  otherwise,  that  we  cannot  regard  the 
inferior  development  of  humanity  in  the  tropics  as 
due  solely  to  temperature.  Physically  considered, 
no  men  attain  a  better  development  than  many  tribes 
who  inhabit  the  warmer  regions  of  the  globe.  The 
inferiority  of  the  inhabitants  of  these  regions  in  intel- 
lectual power  is  more  likely  the  result  of  race  heredity 
than  of  temperature. 

We  all  know  that  this  earth  on  which  we  dwell  is 
only  one  of  countless  millions  of  globes  scattered 
through  the  wilds  of  infinite  space.  So  far  as  we 
know,  most  of  these  globes  are  wholly  unlike  the 
earth,  being  at  a  temperature  so  high  that,  like  our 

121 


SIDE-LIGHTS    ON    ASTRONOMY 

sun,  they  shine  by  their  own  light.  In  such  worlds 
we  may  regard  it  as  quite  certain  that  no  organized 
life  could  exist.  But  evidence  is  continually  in- 
creasing that  dark  and  opaque  worlds  like  ours  exist 
and  revolve  around  their  suns,  as  the  earth  on  which 
we  dwell  revolves  around  its  central  luminary.  Al- 
though the  number  of  such  globes  yet  discovered  is 
not  great,  the  circumstances  under  which  they  are 
found  lead  us  to  believe  that  the  actual  number  may 
be  as  great  as  that  of  the  visible  stars  which  stud  the 
sky.  If  so,  the  probabilities  are  that  millions  of 
them  are  essentially  similar  to  our  own  globe.  Have1 
we  any  reason  to  believe  that  life  exists  on  these 
other  worlds? 

The  reader  will  not  expect  me  to  answer  this  ques- 
tion positively.  It  must  be  admitted  that,  scientifi- 
cally, we  have  no  light  upon  the  question,  and  there- 
fore no  positive  grounds  for  reaching  a  conclusion. 
We  can  only  reason  by  analogy  and  by  what  we  know 
of  the  origin  and  conditions  of  life  around  us,  and 
assume  that  the  same  agencies  which  are  at  play  here 
would  be  found  at  play  under  similar  conditions  in] 
other  parts  of  the  universe. 

If  we  ask  what  the  opinion  of  men  has  been,  we; 
know  historically  that  our  race  has,  in  all  periods  of 
its  history,  peopled  other  regions  with  beings  even 
higher  in  the  scale  of  development  than  we  are  our- 
selves. The  gods  and  demons  of  an  earlier  age  all 
wielded  powers  greater  than  those  granted  to  man — 
powers  which  they  could  use  to  determine  human 
destiny.  But,  up  to  the  time  that  Copernicus  showed 
that  the  planets  were  other  worlds,  the  location  of 
these  imaginary  beings  was  rather  indefinite.  It  was 
therefore  quite  natural  that  when  the  moon  and 

122 


LIFE    IN    THE    UNIVERSE 

planets  were  found  to  be  dark  globes  of  a  size  com- 
parable with  that  of  the  earth  itself,  they  were  made 
the  habitations  of  beings  like  unto  ourselves. 

The  trend  of  modern  discovery  has  been  against 
carrying  this  view  to  its  extreme,  as  will  be  present- 
ly shown.  Before  considering  the  difficulties  in  the 
way  of  accepting  it  to  the  widest  extent,  let  us  enter 
upon  some  preliminary  considerations  as  to  the  origin 
and  prevalence  of  life,  so  far  as  we  have  any  sound 
basis  to  go  upon. 

A  generation  ago  the  origin  of  life  upon  our  planet 
was  one  of  the  great  mysteries  of  science.  All  the 
facts  brought  out  by  investigation  into  the  past  his- 
tory of  our  earth  seemed  to  show,  with  hardly  the 
possibility  of  a  doubt,  that  there  was  a  time  when  it 
was  a  fiery  mass,  no  more  capable  of  serving  as  the 
abode  of  a  living  being  than  the  interior  of  a  Bessemer 
steel  furnace.  There  must  therefore  have  been, 
within  a  certain  period,  a  beginning  of  life  upon  its 
surface.  But,  so  far  as  investigation  had  gone — 
indeed,  so  far  as  it  has  gone  to  the  present  time — no 
life  has  been  found  to  originate  of  itself.  The  living 
germ  seems  to  be  necessary  to  the  beginning  of  any 
living  form.  Whence,  then,  came  the  first  germ? 
Many  of  our  readers  may  remember  a  suggestion 
by  Sir  William  Thomson,  now  Lord  Kelvin,  made 
twenty  or  thirty  years  ago,  that  life  may  have  been 
brought  to  our  planet  by  the  falling  of  a  meteor  from 
space.  This  does  not,  however,  solve  the  difficulty 
—indeed,  it  would  only  make  it  greater.  It  still 
leaves  open  the  question  how  life  began  on  the 
meteor ;  and  granting  this,  why  it  was  not  destroyed 
by  the  heat  generated  as  the  meteor  passed  through 
the  air.  The  popular  view  that  life  began  through  / 

123 


SIDE-LIGHTS    ON    ASTRONOMY 

a  special  act  of  creative  power  seemed  to  be  almost 
[^  forced  upon  man  by  the  failure  of  science  to  discover 
any  other  beginning  for  it.  It  cannot  be  said  that 
even  to-day  anything  definite  has  been  actually  dis- 
covered to  refute  this  view.  All  we  can  say  about 
it  is  that  it  does  not  run  in  with  the  general  views  of 
modern  science  as  to  the  beginning  of  things,  and  that 
those  who  refuse  to  accept  it  must  hold  that,  under 
certain  conditions  which  prevail,  life  begins  by  a  very 
gradual  process,  similar  to  that  by  which  forms  sug- 
gesting growth  seem  to  originate  even  under  conditions 
so  unfavorable  as  those  existing  in  a  bottle  of  acid. 

But  it  is  not  at  all  necessary  for  our  purpose  to 
decide  this  question.  If  life  existed  through  a  crea- 
tive act,  it  is  absurd  to  suppose  that  that  act  was 
confined  to  one  of  the  countless  millions  of  worlds 
scattered  through  space.  If  it  began  at  a  certain 
stage  of  evolution  by  a  natural  process,  the  question 
will  arise,  what  conditions  are  favorable  to  the  com- 
mencement of  this  process?  Here  we  are  quite  jus- 
tified in  reasoning  from  what,  granting  this  process, 
has  taken  place  upon  our  globe  during  its  past  his- 
tory. One  of  the  most  elementary  principles  ac- 
cepted by  the  human  mind  is  that  like  causes  pro- 
duce like  effects.  The  special  conditions  under  which 
we  find  life  to  develop  around  us  may  be  compre- 
hensively summed  up  as  the  existence  of  water  in 
the  liquid  form,  and  the  presence  of  nitrogen,  free 
perhaps  in  the  first  place,  but  accompanied  by  sub- 
stances with  which  it  may  form  combinations.  Oxy- 
gen, hydrogen,  and  nitrogen  are,  then,  the  funda- 
mental requirements.  The  addition  of  calcium  or 
other  forms  of  matter  necessary  to  the  existence  of 
a  solid  world  goes  without  saying.  The  question  now 

124 


LIFE    IN    THE    UNIVERSE 

is  whether  these  necessary  conditions  exist  in  other 
parts  of  the  universe. 

The  spectroscope  shows  that,  so  far  as  the  chemical 
elements  go,  other  worlds  are  composed  of  the  same 
elements  as  ours.  Hydrogen  especially  exists  every- 
where, and  we  have  reason  to  believe  that  the  same 
is  true  of  oxygen  and  nitrogen.  Calcium,  the  base 
of  lime,  is  almost  universal.  So  far  as  chemical  ele- 
ments go,  we  may  therefore  take  it  for  granted  that 
the  conditions  under  which  life  begins  are  very  wide- 
ly diffused  in  the  universe.  It  is,  therefore,  contrary 
to  all  the  analogies  of  nature  to  suppose  that  life  be- 
gan only  on  a  single  world. 

It  is  a  scientific  inference,  based  on  facts  so  nu- 
merous as  not  to  admit  of  serious  question,  that  dur- 
ing the  history  of  our  globe  there  has  been  a  continu- 
ally improving  development  of  life.  As  ages  upon 
ages  pass,  new  forms  are  generated,  higher  in  the 
scale  than  those  which  preceded  them,  until  at  length 
reason  appears  and  asserts  its  sway.  In  a  recent 
well-known  work  Alfred  Russel  Wallace  has  argued 
that  this  development  of  life  required  the  presence 
of  such  a  rare  combination  of  conditions  that  there 
is  no  reason  to  suppose  that  it  prevailed  anywhere 
except  on  our  earth.  It  is  quite  impossible  in  the 
present  discussion  to  follow  his  reasoning  in  detail; 
but  it  seems  to  me  altogether  inconclusive.  Not 
only  does  life,  but  intelligence,  flourish  on  this  globe 
under  a  great  variety  of  conditions  as  regards  tem- 
perature and  surroundings,  and  no  sound  reason  can 
be  shown  why  under  certain  conditions,  which  are 
frequent  in  the  universe,  intelligent  beings  should 
not  acquire  the  highest  development. 

Now  let  us  look  at  the  subject  from  the  view  of 

125 


SIDE-LIGHTS    ON    ASTRONOMY 

the  mathematical  theory  of  probabilities.  A  funda- 
mental tenet  of  this  theory  is  that  no  matter  how  im- 
probable a  result  may  be  on  a  single  trial,  supposing 
it  at  all  possible,  it  is  sure  to  occur  after  a  sufficient 
number  of  trials — and  over  and  over  again  if  the  trials 
are  repeated  often  enough.  For  example,  if  a  million 
grains  of  corn,  of  which  a  single  one  was  red,  were  all 
placed  in  a  pile,  and  a  blindfolded  person  were  re- 
quired to  grope  in  the  pile,  select  a  grain, 'and  then 
put  it  back  again,  the  chances  would  be  a  million  to 
one  against  his  drawing  out  the  red  grain.  If  draw- 
ing it  meant  he  should  die,  a  sensible  person  would 
give  himself  no  concern  at  having  to  draw  the  grain. 
The  probability  of  his  death  would  not  be  so  great 
as  the  actual  probability  that  he  will  really  die  within 
the  next  twenty-four  hours.  And  yet  if  the  whole 
human  race  were  required  to  run  this  chance,  it  is 
certain  that  about  fifteen  hundred,  or  one  out  of  a 
million,  of  the  whole  human  family  would  draw  the 
red  grain  and  meet  his  death. 

Now  apply  this  principle  to  the  universe.  Let  us 
suppose,  to  fix  the  ideas,  that  there  are  a  hundred 
million  worlds,  but  that  the  chances  are  one  thou- 
sand to  one  against  any  one  of  these  taken  at  ran- 
dom being  fitted  for  the  highest  development  of  life 
or  for  the  evolution  of  reason.  The  chances  would 
still  be  that  one  hundred  thousand  of  them  would 
be  inhabited  by  rational  beings  whom  we  call  human. 
But  where  are  we  to  look  for  these  worlds  ?  This  no 
man  can  tell.  We  only  infer  from  the  statistics  of 
the  stars — and  this  inference  is  fairly  well  grounded 
—that  the  number  of  worlds  which,  so  far  as  we 
know,  may  be  inhabited,  are  to  be  counted  by  thou- 
sands, and  perhaps  by  millions. 

126 


LIFE    IN    THE    UNIVERSE 

In  a  number  of  bodies  so  vast  we  should  expect 
every  variety  of  conditions  as  regards  temperature 
and  surroundings.  If  we  suppose  that  the  special 
conditions  which  prevail  on  our  planet  are  necessary 
to  the  highest  forms  of  life,  we  still  have  reason  to 
believe  that  these  same  conditions  prevail  on  thou- 
sands of  other  worlds.  The  fact  that  we  might  find 
the  conditions  in  millions  of  other  worlds  unfavorable 
to  life  would  not  disprove  the  existence  of  the  latter 
on  countless  worlds  differently  situated. 

Coming  down  now  from  the  general  question  to 
the  specific  one,  we  all  know  that  the  only  worlds  the 
conditions  of  which  can  be  made  the  subject  of  ob- 
servation are  the  planets  which  revolve  around  the 
sun,  and  their  satellites.  The  question  whether  these 
bodies  are  inhabited  is  one  which,  of  course,  com- 
pletely transcends  not  only  our  powers  of  observation 
at  present,  but  every  appliance  of  research  that  we 
can  conceive  of  men  devising.  If  Mars  is  inhabited, 
and  if  the  people  of  that  planet  have  equal  powers 
with  ourselves,  the  problem  of  merely  producing  an 
illumination  which  could  be  seen  in  our  most  power- 
ful telescope  would  be  beyond  all  the  ordinary  efforts 
of  an  entire  nation.  An  unbroken  square  mile  of 
flame  would  be  invisible  in  our  telescopes,  but  a 
hundred  square  miles  might  be  seen.  We  cannot, 
therefore,  expect  to  see  any  signs  of  the  works  of 
inhabitants  even  on  Mars.  All  that  we  can  do  is  to 
ascertain  with  greater  or  less  probability  whether  the 
conditions  necessary  to  life  exist  on  the  other  planets 
of  the  system. 

The  moon  being  much  the  nearest  to  us  of  all  the 
heavenly  bodies,  we  can  pronounce  more  definitely 
in  its  case  than  in  any  other.  We  know  that  neither 

127 


SIDE-LIGHTS    ON    ASTRONOMY 

air  nor  water  exists  on  the  moon  in  quantities  suf- 
ficient to  be  perceived  by  the  most  delicate  tests  at 
our  command.  It  is  certain  that  the  moon's  atmos- 
phere, if  any  exists,  is  less  than  the  thousandth  part 
of  the  density  of  that  around  us.  The  vacuum  is 
greater  than  any  ordinary  air-pump  is  capable  of 
producing.  We  can  hardly  suppose  that  so  small  a 
quantity  of  air  could  be  of  any  benefit  whatever  in 
sustaining  life;  an  animal  that  could  get  along  on  so 
little  could  get  along  on  none  at  all. 

But  the  proof  of  the  absence  of  life  is  yet  stronger 
when  we  consider  the  results  of  actual  telescopic  ob- 
servation. An  object  such  as  an  ordinary  city  block 
could  be  detected  on  the  moon.  If  anything  like 
vegetation  were  present  on  its  surface,  we  should  see 
the  changes  which  it  would  undergo  in  the  course  of 
a  month,  during  one  portion  of  which  it  would  be 
exposed  to  the  rays  of  the  unclouded  sun,  and  during 
another  to  the  intense  cold  of  space.  If  men  built 
cities,  or  even  separate  buildings  the  size  of  the  larger 
ones  on  our  earth,  we  might  see  some  signs  of  them. 

In  recent  times  we  not  only  observe  the  moon  with 
the  telescope,  but  get  still  more  definite  information 
by  photography.  The  whole  visible  surface  has  been 
repeatedly  photographed  under  the  best  conditions. 
But  no  change  has  been  established  beyond  question, 
nor  does  the  photograph  show  the  slightest  difference 
of  structure  or  shade  which  could  be  attributed  to 
cities  or  other  works  of  man.  To  all  appearances  the 
whole  surface  of  our  satellite  is  as  completely  devoid 
of  life  as  the  lava  newly  thrown  from  Vesuvius. 

We  next  pass  to  the  planets.  Mercury,  the  near- 
est to  the  sun,  is  in  a  position  very  unfavorable  for 
observation  from  the  earth,  because  when  nearest 

128 


LIFE    IN    THE    UNIVERSE 

to  us  it  is  between  us  and  the  sun,  so  that  its  dark 
hemisphere  is  presented  to  us.  Nothing  satisfactory 
has  yet  been  made  out  as  to  its  condition.  We  can- 
not say  with  certainty  whether  it  has  an  atmosphere 
or  not.  What  seems  very  probable  is  that  the  tem- 
perature on  its  surface  is  higher  than  any  of  our 
earthly  animals  could  sustain.  But  this  proves 
nothing. 

We  know  that  Venus  has  an  atmosphere.  This 
was  very  conclusively  shown  during  the  transits  of 
Venus  in  1874  and  1882.  But  this  atmosphere  is 
so  filled  with  clouds  or  vapor  that  it  does  not  seem 
likely  that  we  ever  get  a  view  of  the  solid  body  of  the 
planet  through  it.  Some  observers  have  thought 
they  could  see  spots  on  Venus  day  after  day,  while 
others  have  disputed  this  view.  On  the  whole,  if 
intelligent  inhabitants  live  there,  it  is  not  likely  that 
they  ever  see  sun  or  stars.  Instead  of  the  sun  they 
see  only  an  effulgence  in  the  vapory  sky  which  dis- 
appears and  reappears  at  regular  intervals. 

When  we  come  to  Mars,  we  have  more  definite 
knowledge,  and  there  seems  to  be  greater  possibilities 
for  life  there  than  in  the  case  of  any  other  planet  be- 
sides the  earth.  The  main  reason  for  denying  that 
life  such  as  ours  could  exist  there  is  that  the  atmos- 
phere of  Mars  is  so  rare  that,  in  the  light  of  the  most 
recent  researches,  we  cannot  be  fully  assured  that  it 
exists  at  all.  The  very  careful  comparisons  of  the 
spectra  of  Mars  and  of  the  moon  made  by  Campbell 
at  the  Lick  Observatory  failed  to  show  the  slightest 
difference  in  the  two.  If  Mars  had  an  atmosphere 
as  dense  as  ours,  the  result  could  be  seen  in  the  dark- 
ening of  the  lines  of  the  spectrum  produced  by  the 
double  passage  of  the  light  through  it.  There  were 

129 


SIDE-LIGHTS    ON    ASTRONOMY 

no  lines  in  the  spectrum  of  Mars  that  were  not  seen 
with  equal  distinctness  in  that  of  the  moon.  But 
this  does  not  prove  the  entire  absence  of  an  atmos- 
phere. It  only  shows  a  limit  to  its  density.  It  may 
be  one-fifth  or  one-fourth  the  density  of  that  on  the 
earth,  but  probably  no  more. 

That  there  must  be  something  in  the  nature  of 
vapor  at  least  seems  to  be  shown  by  the  formation 
and  disappearance  of  the  white  polar  caps  of  this 
planet.  Every  reader  of  astronomy  at  the  present 
time  knows  that,  during  the  Martian  winter,  white 
caps  form  around  the  pole  of  the  planet  which  is 
turned  away  from  the  sun,  and  grow  larger  and 
larger  until  the  sun  begins  to  shine  upon  them,  when 
they  gradually  grow  smaller,  and  perhaps  nearly  dis- 
appear. It  seems,  therefore,  fairly  well  proved  that, 
under  the  influence  of  cold,  some  white  substance 
forms  around  the  polar  regions  of  Mars  which  evapo- 
rates under  the  influence  of  the  sun's  rays.  It  has 
been  supposed  that  this  substance  is  snow,  produced 
in  the  same  way  that  snow  is  produced  on  the  earth, 
by  the  evaporation  of  water. 

But  there  are  difficulties  in  the  way  of  this  ex- 
planation. The  sun  sends  less  than  half  as  much 
heat  to  Mars  as  to  the  earth,  and  it  does  not  seem 
likely  that  the  polar  regions  can  ever  receive  enough 
of  heat  to  melt  any  considerable  quantity  of  snow. 
Nor  does  it  seem  likely  that  any  clouds  from  which 
snow  could  fall  ever  obscure  the  surface  of  Mars. 

But  a  very  slight  change  in  the  explanation  will 
make  it  tenable.  Quite  possibly  the  white  deposits 
may  be  due  to  something  like  hoar-frost  condensed 
from  slightly  moist  air,  without  the  actual  production 
of  snow.  This  would  produce  the  effect  that  we  see. 

130 


LIFE    IN    THE    UNIVERSE 

Even  this  explanation  implies  that  Mars  has  air  and 
water,  rare  though  the  former  may  be.  It  is  quite 
possible  that  air  as  thin  as  that  of  Mars  would  sus- 
tain life  in  some  form.  Life  not  totally  unlike  that 
on  the  earth  may  therefore  exist  upon  this  planet  for 
anything  that  we  know  to  the  contrary.  More  than 
this  we  cannot  say. 

In  the  case  of  the  outer  planets  the  answer  to  our 
question  must  be  in  the  negative.  It  now  seems 
likely  that  Jupiter  is  a  body  very  much  like  our  sun, 
only  that  the  dark  portion  is  too  cool  to  emit  much, 
if  any,  light.  It  is  doubtful  whether  Jupiter  has  any- 
thing in  the  nature  of  a  solid  surface.  Its  interior 
is  in  all  likelihood  a  mass  of  molten  matter  far  above 
a  red  heat,  which  is  surrounded  by  a  comparatively 
cool,  yet,  to  our  measure,  extremely  hot,  vapor.  The 
beltlike  clouds  which  surround  the  planet  are  due  to 
this  vapor  combined  with  the  rapid  rotation.  If 
there  is  any  solid  surface  below  the  atmosphere  that 
we  can  see,  it  is  swept  by  winds  such  that  nothing  we 
have  on  earth  could  withstand  them.  But,  as  we 
have  said,  the  probabilities  are  very  much  against 
there  being  anything  like  such  a  surface.  At  some 
great  depth  in  the  fiery  vapor  there  is  a  solid  nucleus ; 
that  is  all  we  can  say. 

The  planet  Saturn  seems  to  be  very  much  like  that 
of  Jupiter  in  its  composition.  It  receives  so  little  heat 
from  the  sun  that,  unless  it  is  a  mass  of  fiery  vapor 
like  Jupiter,  the  surface  must  be  far  below  the  freez- 
ing-point. 

We  cannot  speak  with  such  certainty  of  Uranus 
and  Neptune;  yet  the  probability  seems  to  be  that 
they  are  in  much  the  same  condition  as  Saturn.  They 
are  known  to  have  very  dense  atmospheres,  which 


SIDE-LIGHTS    ON    ASTRONOMY 

are  made  known  to  us  only  by  their  absorbing  some 
of  the  light  of  the  sun.  But  nothing  is  known  of  the 
compositon  of  these  atmospheres. 

To  sum  up  our  argument:  the  fact  that,  so  far  as 
we  have  yet  been  able  to  learn,  only  a  very  small 
proportion  of  the  visible  worlds  scattered  through 
space  are  fitted  to  be  the  abode  of  life  does  not  pre- 
clude the  probability  that  among  hundreds  of  millions 
of  such  worlds  a  vast  number  are  so  fitted.  Such 
being  the  case,  all  the  analogies  of  nature  lead  us  to 
believe  that,  whatever  the  process  which  led  to  life 
upon  this  earth — whether  a  special  act  of  creative 
power  or  a  gradual  course  of  development — through 
that  same  process  does  life  begin  in  every  part  of  the 
universe  fitted  to  sustain  it.  The  course  of  develop- 
ment involves  a  gradual  improvement  in  living  forms, 
which  by  irregular  steps  rise  higher  and  higher  in  the 
scale  of  being.  We  have  every  reason  to  believe  that 
this  is  the  case  wherever  life  exists.  It  is,  therefore, 
perfectly  reasonable  to  suppose  that  beings,  not  only 
animated,  but  endowed  with  reason,  inhabit  count- 
less worlds  in  space.  It  would,  indeed,  be  very  in- 
spiring could  we  learn  by  actual  observation  what 
forms  of  society  exist  throughout  space,  and  see  the 
members  of  such  societies  enjoying  themselves  by 
their  warm  firesides.  But  this,  so  far  as  we  can  now 
see,  is  entirely  beyond  the  possible  reach  of  our 
race,  so  long  as  it  is  confined  to  a  single  world. 


VIII 
HOW   THE   PLANETS   ARE   WEIGHED 

YOU  ask  me  how  the  planets  are  weighed?  I  re- 
ply, on  the  same  principle  by  which  a  butcher 
weighs  a  ham  in  a  spring-balance.  When  he  picks 
the  ham  up,  he  feels  a  pull  of  the  ham  towards  the 
earth.  When  he  hangs  it  on  the  hook,  this  pull  is 
transferred  from  his  hand  to  the  spring  of  the  balance. 
The  stronger  the  pull,  the  farther  the  spring  is  pulled 
down.  What  he  reads  on  the  scale  is  the  strength 
of  the  pull.  You  know  that  this  pull  is  simply  the 
attraction  of  the  earth  on  the  ham.  But,  by  a  uni- 
versal law  of  force,  the  ham  attracts  the  earth  exact- 
ly as  much  as  the  earth  does  the  ham.  So  what  the 
butcher  really  does  is  to  find  how  much  or  how 
strongly  the  ham  attracts  the  earth,  and  he  calls 
that  pull  the  weight  of  the  ham.  On  the  same  prin- 
ciple, the  astronomer  finds  the  weight  of  a  body  by 
finding  how  strong  is  its  attractive  pull  on  some 
other  body.  If  the  butcher,  with  his  spring-balance 
and  a  ham,  could  fly  to  all  the  planets,  one  after  the 
other,  weigh  the  ham  on  each,  and  come  back  to  re- 
port the  results  to  an  astronomer,  the  latter  could 
immediately  compute  the  weight  of  each  planet  of 
known  diameter,  as  compared  with  that  of  the  earth. 
In  applying  this  principle  to  the  heavenly  bodies, 
we  at  once  meet  a  difficulty  that  looks  insurmount- 


SIDE-LIGHTS    ON    ASTRONOMY 

able.  You  cannot  get  up  to  the  heavenly  bodies  to 
do  your  weighing;  how  then  will  you  measure  their 
pull?  I  must  begin  the  answer  to  this  question  by 
explaining  a  nice  point  in  exact  science.  Astronomers 
distinguish  between  the  weight  of  a  body  and  its  mass. 
The  weight  of  objects  is  not  the  same  all  over  the 
world;  a  thing  which  weighs  thirty  pounds  in  New 
York  would  weigh  an  ounce  more  than  thirty  pounds 
in  a  spring-balance  in  Greenland,  and  nearly  an  ounce 
less  at  the  equator.  This  is  because  the  earth  is  not 
a  perfect  sphere,  but  a  little  flattened.  Thus  weight 
varies  with  the  place.  If  a  ham  weighing  thirty 
pounds  were  taken  up  to  the  moon  and  weighed  there, 
the  pull  would  only  be  five  pounds,  because  the  moon 
is  so  much  smaller  and  lighter  than  the  earth.  There 
would  be  another  weight  of  the  ham  for  the  planet 
Mars,  and  yet  another  on  the  sun,  where  it  would 
weigh  some  eight  hundred  pounds.  Hence  the  as- 
tronomer does  not  speak  of  the  weight  of  a  planet, 
because  that  would  depend  on  the  place  where  it  was 
weighed;  but  he  speaks  of  the  mass  of  the  planet,; 
which  means  how  much  planet  there  is,  no  matter 
where  you  might  weigh  it. 

At  the  same  time,  we  might,  without  any  inexact- 
ness, agree  that  the  mass  of  a  heavenly  body  should 
be  fixed  by  the  weight  it  would  have  in  New  York. 
As  we  could  not  even  imagine  a  planet  at  New  York, 
because  it  may  be  larger  than  the  earth  itself,  what 
we  are  to  imagine  is  this:  Suppose  the  planet  could 
be  divided  into  a  million  million  million  equal  parts,  \ 
and  one  of  these  parts  brought  to  New  York  and 
weighed.  We  could  easily  find  its  weight  in  pounds 
or  tons.  Then  multiply  this  weight  by  a  million 
million  million,  and  we  shall  have  a  weight  of  the 

134 


HOW  THE  PLANETS  ARE  WEIGHED 

planet.     This  would  be  what  the  astronomers  might 
take  as  the  mass  of  the  planet. 

With  these  explanations,  let  us  see  how  the  weight 
of  the  earth  is  found.  The  principle  we  apply  is  that 
round  bodies  of  the  same  specific  gravity  attract  small 
objects  on  their  surface  with  a  force  proportional  to 
the  diameter  of  the  attracting  body.  For  example,  a 
body  two  feet  in  diameter  attracts  twice  as  strongly 
as  one  of  a  foot,  one  of  three  feet  three  times  as 
strongly,  and  so  on.  Now,  our  earth  is  about  40,000,- 
ooo  feet  in  diameter;  that  is  10,000,000  times  four 
feet.  It  follows  that  if  we  made  a  little  model  of  the 
earth  four  feet  in  diameter,  having  the  average  specific 
gravity  of  the  earth,  it  would  attract  a  particle  with 
one  ten-millionth  part  of  the  attraction  of  the  earth. 
The  attraction  of  such  a  model  has  actually  been 
measured.  Since  we  do  not  know  the  average 
specific  gravity  of  the  earth — that  being  in  fact  what 
we  want  to  find  out  —  we  take  a  globe  of  lead,  four 
feet  in  diameter,  let  us  suppose.  By  means  of  a 
balance  of  the  most  exquisite  construction  it  is 
found  that  such  a  globe  does  exert  a  minute  attrac- 
tion on  small  bodies  around  it,  and  that  this  attrac- 
tion is  a  little  more  than  the  ten-millionth  part  of 
that  of  the  earth.  This  shows  that  the  specific  grav- 
ity of  the  lead  is  a  little  greater  than  that  of  the 
average  of  the  whole  earth.  All  the  minute  calcula- 
tions made,  it  is  found  that  the  earth,  in  order  to 
attract  with  the  force  it  does,  must  be  about  five 
and  one-half  times  as  heavy  as  its  bulk  of  water,  or 
perhaps  a  little  more.  Different  experimenters  find 
different  results;  the  best  between  5.5  and  5.6,  so 
that  5.5  is,  perhaps,  as  near  the  number  as  we  can 
now  get.  This  is  much  more  than  the  average 


SIDE-LIGHTS    ON    ASTRONOMY 

specific  gravity  of  the  materials  which  compose  that 
part  of  the  earth  which  we  can  reach  by  digging 
mines.  The  difference  arises  from  the  fact  that,  at 
the  depth  of  many  miles,  the  matter  composing  the 
earth  is  compressed  into  a  smaller  space  by  the 
enormous  weight  of  the  portions  lying  above  it. 
Thus,  at  the  depth  of  1000  miles,  the  pressure  on 
every  cubic  inch  is  more  than  2000  tons,  a  weight 
which  would  greatly  condense  the  hardest  metal. 

We  come  now  to  the  planets.  I  have  said  that  the 
mass  or  weight  of  a  heavenly  body  is  determined  by 
its  attraction  on  some  other  body.  There  are  two 
ways  in  which  the  attraction  of  a  planet  may  be 
measured.  One  is  by  its  attraction  on  the  planets 
next  to  it.  If  these  bodies  did  not  attract  one  an- 
other at  all,  but  only  moved  under  the  influence  of 
the  sun,  they  would  move  in  orbits  having  the  form 
of  ellipses.  They  are  found  to  move  very  nearly  in 
such  orbits,  only  the  actual  path  deviates  from  an 
ellipse,  now  in  one  direction  and  then  in  another, 
and  it  slowly  changes  its  position  from  year  to  year. 
These  deviations  are  due  to  the  pull  of  the  other 
planets,  and  by  measuring  the  deviations  we  can 
determine  the  amount  of  the  pull,  and  hence  the  mass 
of  the  planet. 

The  reader  will  readily  understand  that  the  mathe- 
matical processes  necessary  to  get  a  result  in  this  way 
must  be  very  delicate  and  complicated.  A  much 
simpler  method  can  be  used  in  the  case  of  those 
planets  which  have  satellites  revolving  round  them, 
because  the  attraction  of  the  planet  can  be  deter- 
mined by  the  motions  of  the  satellite.  The  first 
law  of  motion  teaches  us  that  a  body  in  motion,  if 
acted  on  by  no  force,  will  move  in  a  straight  line. 

136 


HOW  THE  PLANETS  ARE  WEIGHED 

Hence,  if  we  see  a  body  moving  in  a  curve,  we  know 
that  it  is  acted  on  by  a  force  in  the  direction  towards 
which  the  motion  curves.  A  familiar  example  is  that 
of  a  stone  thrown  from  the  hand.  If  the  stone  were 
not  attracted  by  the  earth,  it  would  go  on  forever  in 
the  line  of  throw,  and  leave  the  earth  entirely.  But 
under  the  attraction  of  the  earth,  it  is  drawn  down 
and  down,  as  it  travels  onward,  until  finally  it  reaches 
the  ground.  The  faster  the  stone  is  thrown,  of  course, 
the  farther  it  will  go,  and  the  greater  will  be  the 
sweep  of  the  curve  of  its  path.  If  it  were  a  cannon- 
ball,  the  first  part  of  the  curve  would  be  nearly  a 
right  line.  If  we  could  fire  a  cannon-ball  horizon- 
tally from  the  top  of  a  high  mountain  with  a  velocity 
of  five  miles  a  second,  and  if  it  were  not  resisted  by 
the  air,  the  curvature  of  the  path  would  be  equal  to 
that  of  the  surface  of  our  earth,  and  so  the  ball  would 
never  reach  the  earth,  but  would  revolve  round  it 
like  a  little  satellite  in  an  orbit  of  its  own.  Could 
this  be  done,  the  astronomer  would  be  able,  knowing 
the  velocity  of  the  ball,  to  calculate  the  attraction 
of  the  earth  as  well  as  we  determine  it  by  actually 
observing  the  motion  of  falling  bodies  around  us. 

Thus  it  is  that  when  a  planet,  like  Mars  or  Ju- 
piter, has  satellites  revolving  round  it,  astronomers 
on  the  earth  can  observe  the  attraction  of  the  planet 
on  its  satellites  and  thus  determine  its  mass.  The 
rule  for  doing  this  is  very  simple.  The  cube  of  the 
distance  between  the  planet  and  satellite  is  divided 
by  the  square  of  the  time  of  revolution  of  the  satel- 
lite. The  quotient  is  a  number  which  is  proportional 
to  the  mass  of  the  planet.  The  rule  applies  to  the 
motion  of  the  moon  round  the  earth  and  of  the 
planets  round  the  sun.  If  we  divide  the  cube  of  the 


SIDE-LIGHTS    ON    ASTRONOMY 

earth's  distance  from  the  sun,  say  93,000,000  miles, 
by  the  square  of  365^,  the  days  in  a  year,  we  shall 
get  a  certain  quotient.  Let  us  call  this  number  the 
sun -quotient.  Then,  if  we  divide  the  cube  of  the 
moon's  distance  from  the  earth  by  the  square  of  its 
time  of  revolution,  we  shall  get  another  quotient, 
which  we  may  call  the  earth-quotient.  The  sun- 
quotient  will  come  out  about  330,000  times  as  large 
as  the  earth-quotient.  Hence  it  is  concluded  that 
the  mass  of  the  sun  is  330,000  times  that  of  the 
earth;  that  it  would  take  this  number  of  earths  to 
make  a  body  as  heavy  as  the  sun. 

I  give  this  calculation  to  illustrate  the  principle; 
it  must  not  be  supposed  that  the  astronomer  pro- 
ceeds exactly  in  this  way  and  has  only  this  simple 
calculation  to  make.  In  the  case  of  the  moon  and 
earth,  the  motion  and  distance  of  the  former  vary 
in  consequence  of  the  attraction  of  the  sun,  so 
that  their  actual  distance  apart  is  a  changing  quan- 
tity. So  what  the  astronomer  actually  does  is  to 
find  the  attraction  of  the  earth  by  observing  the 
length  of  a  pendulum  which  beats  seconds  in  various 
latitudes.  Then,  by  very  delicate  mathematical 
processes,  he  can  find  with  great  exactness  what 
would  be  the  time  of  revolution  of  a  small  satellite 
at  any  given  distance  from  the  earth,  and  thus  can 
get  the  earth-quotient. 

But,  as  I  have  already  pointed  out,  we  must,  in 
the  case  of  the  planets,  find  the  quotient  in  question 
by  means  of  the  satellites ;  and  it  happens,  fortunate- 
ly, that  the  motions  of  these  bodies  are  much  less 
changed  by  the  attraction  of  the  sun  than  is  the 
motion  of  the  moon.  Thus,  when  we  make  the 
computation  for  the  outer  satellite  of  Mars,  we  find 

138 


HOW  THE  PLANETS  ARE  WEIGHED 

the  quotient  to  be  309*soo  that  of  the  sun  -  quotient. 
Hence  we  conclude  that  the  mass  of  Mars  is 


3093500 


that  of  the  sun.  By  the  corresponding  quotient, 
the  mass  of  Jupiter  is  found  to  be  about  -—-  that  of 
the  sun,  Saturn  ^,  Uranus  ^,  Neptune 


We  have  set  forth  only  the  great  principle  on 
which  the  astronomer  has  proceeded  for  the  pur- 
pose in  question.  The  law  of  gravitation  is  at  the 
bottom  of  all  his  work.  The  effects  of  this  law  re- 
quire mathematical  processes  which  it  has  taken  two 
hundred  years  to  bring  to  their  present  state,  and 
which  are  still  far  from  perfect.  The  measurement 
of  the  distance  of  a  satellite  is  not  a  job  to  be  done 
in  an  evening;  it  requires  patient  labor  extending 
through  months  and  years,  and  then  is  not  as  exact 
as  the  astronomer  would  wish.  He  does  the  best  he 
can,  and  must  be  satisfied  with  that. 


IX 

THE    MARINER'S    COMPASS 

A^ONG  those  provisions  of  Nature  which  seem 
to  us  as  especially  designed  for  the  use  of  man, 
none  is  more  striking  than  the  seeming  magnetism 
of  the  earth.  What  would  our  civilization  have  been 
if  the  mariner's  compass  had  never  been  known? 
That  Columbus  could  never  have  crossed  the  Atlantic 
is  certain ;  in  what  generation  since  his  time  our  con- 
tinent would  have  been  discovered  is  doubtful.  Did 
the  reader  ever  reflect  what  a  problem  the  captain 
of  the  finest  ocean  liner  of  our  day  would  face  if  he 
had  to  cross  the  ocean  without  this  little  instrument  ? 
With  the  aid  of  a  pilot  he  gets  his  ship  outside  of 
Sandy  Hook  without  much  difficulty.  Even  later, 
so  long  as  the  sun  is  visible  and  the  air  is  clear,  he 
will  have  some  apparatus  for  sailing  by  the  direction 
of  the  sun.  But  after  a  few  hours  clouds  cover  the 
sky.  From  that  moment  he  has  not  the  slightest 
idea  of  east,  west,  north,  or  south,  except  so  far  as 
he  may  infer  it  from  the  direction  in  which  he  notices 
the  wind  to  blow.  For  a  few  hours  he  may  be  guided 
by  the  wind,  provided  he  is  sure  he  is  not  going  ashore 
on  Long  Island.  Thus,  in  time,  he  feels  his  way  out 
into  the  open  sea.  By  day  he  has  some  idea  of  di- 
rection with  the  aid  of  the  sun;  by  night,  when  the 
sky  is  clear  he  can  steer  by  the  Great  Bear,  or  "  Cyno- 

140 


THE    MARINER'S    COMPASS 

sure,"  the  compass  of  his  ancient  predecessors  on  the 
Mediterranean.  But  when  it  is  cloudy,  if  he  persists 
in  steaming  ahead,  he  may  be  running  towards  the 
Azores  or  towards  Greenland,  or  he  may  be  making 
his  way  back  to  New  York  without  knowing  it.  So, 
keeping  up  steam  only  when  sun  or  star  is  visible,  he 
at  length  finds  that  he  is  approaching  the  coast  of 
Ireland.  Then  he  has  to  grope  along  much  like  a 
blind  man  with  his  staff,  feeling  his  way  along  the 
edge  of  a  precipice.  He  can  determine  the  latitude 
at  noon  if  the  sky  is  clear,  and  his  longitude  in  the 
morning  or  evening  in  the  same  conditions.  In  this 
way  he  will  get  a  general  idea  of  his  whereabouts. 
But  if  he  ventures  to  make  headway  in  a  fog,  he  may 
find  himself  on  the  rocks  at  any  moment.  He  reaches 
his  haven  only  after  many  spells  of  patient  waiting 
for  favoring  skies. 

The  fact  that  the  earth  acts  like  a  magnet,  that  the 
needle  points  to  the  north,  has  been  generally  known 
to  navigators  for  nearly  a  thousand  years,  and  is  said 
to  have  been  known  to  the  Chinese  at  a  yet  earlier 
period.  And  yet,  to-day,  if  any  professor  of  physical 
science  is  asked  to  explain  the  magnetic  property  of 
the  earth,  he  will  acknowledge  his  inability  to  do  so 
to  his  own  satisfaction.  Happily  this  does  not  hinder 
us  from  finding  out  by  what  law  these  forces  act,  and 
how  they  enable  us  to  navigate  the  ocean.  I  there- 
fore hope  the  reader  will  be  interested  in  a  short  ex- 
position of  the  very  curious  and  interesting  laws  on 
which  the  science  of  magnetism  is  based,  and  which 
are  applied  in  the  use  of  the  compass. 

The  force  known  as  magnetic,  on  which  the  com- 
pass depends,  is  different  from  all  other  natural  forces 
with  which  we  are  familiar.  It  is  very  remarkable 

141 


SIDE-LIGHTS     ON    ASTRONOMY 

that  iron  is  the  only  substance  which  can  become 
magnetic  in  any  considerable  degree.     Nickel  and  one 
of  two  other  metals  have  the  same  property,  but  in 
a  very  slight  degree.     It  is  also  remarkable  that,  how-  ' 
ever  powerfully  a  bar  of  steel  may  be  magnetized,  \ 
not  the  slightest  effect  of  the  magnetism  can  be  seen 
by  its  action  on  other  than  magnetic  substances.     It 
is  no  heavier  than  before.     Its  magnetism  does  not 
produce  the  slightest  influence  upon  the  human  body,  i 
No  one  would  know  that  it  was  magnetic  until  some- 
thing containing  iron  was  brought  into  its  immediate 
neighborhood ;  then  the  attraction  is  set  up. 

The  most  important  principle  of  magnetic  science 
is  that  there  are  two  opposite  kinds  of  magnetism, 
which  are,  in  a  certain  sense,  contrary  in  their  mani- 
festations. The  difference  is  seen  in  the  behavior  of 
the  magnet  itself.  One  particular  end  points  north, 
and  the  other  end  south.  What  is  it  that  distin- 
guishes these  two  ends  ?  The  answer  is  that  one  end 
has  what  we  call  north  magnetism,  while  the  other 
has  south  magnetism.  Every  magnetic  bar  has  tw6 
poles,  one  near  one  end,  one  near  the  other.  The 
north  pole  is  drawn  towards  the  north  pole  of  the 
earth,  the  south  pole  towards  the  south  pole,  and  thus 
it  is  that  the  direction  of  the  magnet  is  determined. 

Now,  when  we  bring  two  magnets  near  each  other 
we  find  another  curious  phenomenon.  If  the  two 
like  poles  are  brought  together,  they  do  not  attract 
but  repel  each  other.  But  the  two  opposite  poles 
attract  each  other.  The  attraction  and  repulsion  are 
exactly  equal  under  the  same  conditions.  There  is 
ho  more  attraction  than  repulsion.  If  we  seal  one 
magnet  up  in  a  paper  or  a  box,  and  then  suspend 
another  over  the  box,  the  north  pole  of  the  one  out- 

142 


THE    MARINER'S    COMPASS 

side  will  tend  to  the  south  pole  of  the  one  in  the  box, 
and  vice  versa. 

Our  next  discovery  is,  that  whenever  a  magnet  at- 
tracts a  piece  of  iron  it  makes  that  iron  into  a  magnet, 
at  least  for  the  time  being.  In  the  case  of  ordinary 
soft  or  untempered  iron  the  magnetism  disappears 
instantly  when  the  magnet  is  removed.  But  if  the 
magnet  be  made  to  attract  a  piece  of  hardened  steel, 
the  latter  will  retain  the  magnetism  produced  in  it 
and  become  itself  a  permanent  magnet. 

This  fact  must  have  been  known  from  the  time 
that  the  compass  came  into  use.  To  make  this  in- 
strument it  was  necessary  to  magnetize  a  small  bar 
or  needle  by  passing  a  natural  magnet  over  it. 

In  our  times  the  magnetization  is  effected  by  an 
electric  current.  The  latter  has  curious  magnetic 
properties ;  a  magnetic  needle  brought  alongside  of  it 
will  be  found  placing  itself  at  right  angles  to  the  wire 
bearing  the  current.  On  this  principle  is  made  the 
galvanometer  for  measuring  the  intensity  of  a  cur- 
rent. Moreover,  if  a  piece  of  wire  is  coiled  round  a 
bar  of  steel,  and  a  powerful  electric  current  pass 
through  the  coil,  the  bar  will  become  a  magnet. 

Another  curious  property  of  magnetism  is  that  we 
cannot  develop  north  magnetism  in  a  bar  without 
developing  south  magnetism  at  the  same  time.  If 
it  were  otherwise,  important  consequences  would  re- 
sult. A  separate  north  pole  of  a  magnet  would,  if 
attached  to  a  floating  object  and  thrown  into  the 
ocean,  start  on  a  journey  towards  the  north  all  by  it- 
self. A  possible  method  of  bringing  this  result  about 
may  suggest  itself.  Let  us  take  an  ordinary  bar 
magnet,  with  a  pole  at  each  end,  and  break  it  in  the 
middle;  then  would  not  the  north  end  be  all  ready 


SIDE-LIGHTS    ON    ASTRONOMY 

to  start  on  its  voyage  north,  and  the  south  end  to 
make  its  way  south?  But,  alas!  when  this  experi- 
ment is  tried  it  is  found  that  a  south  pole  instantly 
develops  itself  on  one  side  of  the  break,  and  a  north 
pole  on  the  other  side,  so  that  the  two  pieces  will 
simply  form  two  magnets,  each  with  its  north  and 
south  pole.  There  is  no  possibility  of  making  a  mag- 
net with  only  one  pole. 

It  was  formerly  supposed  that  the  central  portions 
of  the  earth  consisted  of  an  immense  magnet  directed 
north  and  south.  Although  this  view  is  found,  for 
reasons  which  need  not  be  set  forth  in  detail,  to  be 
untenable,  it  gives  us  a  good  general  idea  of  the  nat- 
ure of  terrestrial  magnetism.  One  result  that  fol- 
lows from  the  law  of  poles  already  mentioned  is  that 
the  magnetism  which  seems  to  belong  to  the  north 
pole  of  the  earth  is  what  we  call  south  on  the  magnet, 
and  vice  versa. 

Careful  experiment  shows  us  that  the  region 
around  every  magnet  is  filled  with  magnetic  force, 
strongest  near  the  poles  of  the  magnet,  but  diminish- 
ing as  the  inverse  square  of  the  distance  from  the 
pole.  This  force,  at  each  point,  acts  along  a  certain 
line,  called  a  line  of  force.  These  lines  are  very 
prettily  shown  by  the  familiar  experiment  of  placing 
a  sheet  of  paper  over  a  magnet,  and  then  scattering 
iron  filings  on  the  surface  of  the  paper.  It  will  be 
noticed  that  the  filings  arrange  themselves  along  a 
series  of  curved  lines,  diverging  in  every  direction 
from  each  pole,  but  always  passing  from  one  pole  to 
the  other.  It  is  a  universal  law  that  whenever  a 
magnet  is  brought  into  a  region  where  this  force  acts, 
it  is  attracted  into  such  a  position  that  it  shall  have 
the  same  direction  as  the  lines  of  force.  Its  north 

144 


THE    MARINER'S    COMPASS 

pole  will  take  the  direction  of  the  curve  leading  to 
the  south  pole  of  the  other  magnet,  and  its  south 
pole  the  opposite  one. 

The  fact  of  terrestrial  magnetism  may  be  expressed 
by  saying  that  the  space  within  and  around  the  whole 
earth  is  filled  by  lines  of  magnetic  force,  which  we 
know  nothing  about  until  we  suspend  a  magnet  so 
perfectly  balanced  that  it  may  point  in  any  direction 
whatever.  Then  it  turns  and  points  in  the  direction 
of  the  lines  of  force,  which  may  thus  be  mapped  out 
for  all  points  of  the  earth. 

We  commonly  say  that  the  pole  of  the  needle  points 
towards  the  north.  The  poets  tell  us  how  the  needle 
is  true  to  the  pole.  Every  reader,  however,  is  now 
familiar  with  the  general  fact  of  a  variation  of  the 
compass.  On  our  eastern  seaboard,  and  all  the  way 
across  the  Atlantic,  the  north  pointing  of  the  com- 
pass varies  so  far  to  the  west  that  a  ship  going  to 
Europe  and  making  no  allowance  for  this  deviation 
would  find  herself  making  more  nearly  for  the  North 
Cape  than  for  her  destination.  The  "declination," 
as  it  is  termed  in  scientific  language,  varies  from  one 
region  of  the  earth  to  another.  In  some  places  it  is 
towards  the  west,  in  others  towards  the  east. 

The  pointing  of  the  needle  in  various  regions  of  the 
world  is  shown  by  means  of  magnetic  maps.  Such 
maps  are  published  by  the  United  States  Coast  Sur- 
vey, whose  experts  make  a  careful  study  of  the  mag- 
netic force  all  over  the  country.  It  is  found  that 
there  is  a  line  running  nearly  north  and  south  through 
the  Middle  States  along  which  there  is  no  variation 
of  the  compass.  To  the  east  of  it  the  variation  of 
the  north  pole  of  the  magnet  is  west ;  to  the  west  of 
it,  east.  The  most  rapid  changes  in  the  pointing  of 


SIDE-LIGHTS    ON    ASTRONOMY 

the  needle  are  towards  the  northeast  and  northwest 
regions.  When  we  travel  to  the  northeastern  boun- 
dary of  Maine  the  westerly  variation  has  risen  to  20°. 
Towards  the  northwest  the  easterly  variation  contin- 
ually increases,  until,  in  the  northern  part  of  the  State 
of  Washington,  it  amounts  to  23°. 

When  we  cross  the  Atlantic  into  Europe  we  find 
the  west  variation  diminishing  until  we  reach  a  cer- 
tain line  passing  through  central  Russia  and  western 
Asia.  This  is  again  a  line  of  no  variation.  Crossing 
it,  the  variation  is  once  more  towards  the  east.  This 
direction  continues  over  most  of  the  continent  of 
Asia,  but  varies  in  a  somewhat  irregular  manner  from 
one  part  of  the  continent  to  another. 

As  a  general  rule,  the  lines  of  the  earth's  magnetic 
force  are  not  horizontal,  and  therefore  one  end  or  the 
other  of  a  perfectly  suspended  magnet  will  dip  below 
the  horizontal  position.  This  is  called  the  "dip  of 
the  needle."  It  is  observed  by  means  of  a  brass 
circle,  of  which  the  circumference  is  marked  off  in 
degrees.  A  magnet  is  attached  to  this  circle  so  as 
to  form  a  diameter,  and  suspended  on  a  horizontal 
axis  passing  through  the  centre  of  gravity,  so  that 
the  magnet  shall  be  free  to  point  in  the  direction  in- 
dicated by  the  earth's  lines  of  magnetic  force.  Armed 
with  this  apparatus,  scientific  travellers  and  naviga- 
tors have  visited  various  points  of  the  earth  in  order 
to  determine  the  dip.  It  is  thus  found  that  there  is 
a  belt  passing  around  the  earth  near  the  equator,  but 
sometimes  deviating  several  degrees  from  it,  in  which 
there  is  no  dip;  that  is  to  say,  the  lines  of  magnetic 
force  are  horizontal.  Taking  any  point  on  this  belt 
and  going  north,  it  will  be  found  that  the  north  pole 
of  the  magnet  gradually  tends  downward,  the  dip 

146 


THE    MARINER'S    COMPASS 

constantly  increasing  as  we  go  farther  north.  In  the 
southern  part  of  the  United  States  the  dip  is  about 
60°,  and  the  direction  of  the  needle  is  nearly  perpen- 
dicular to  the  earth's  axis.  In  the  northern  part  of 
the  country,  including  the  region  of  the  Great  Lakes, 
the  dip  increases  to  75°.  Noticing  that  a  dip  of  90° 
would  mean  that  the  north  end  of  the  magnet  points 
straight  downward,  it  follows  that  it  would  be  more 
nearly  correct  to  say  that,  throughout  the  United 
States,  the  magnetic  needle  points  up  and  down  than 
that  it  points  north  and  south. 

Going  yet  farther  north,  we  find  the  dip  still  in- 
creasing, until  at  a  certain  point  in  the  arctic  regions 
the  north  pole  of  the  needle  points  downward.  In 
this  region  the  compass  is  of  no  use  to  the  traveller 
or  the  navigator.  The  point  is  called  the  Magnetic 
Pole.  Its  position  has  been  located  several  times 
by  scientific  observers.  The  best  determinations 
made  during  the  last  eighty  years  agree  fairly  well 
in  placing  it  near  70°  north  latitude  and  97°  longitude 
west  from  Greenwich.  This  point  is  situated  on  the 
west  shore  of  the  Boothian  Peninsula,  which  is  bound- 
ed on  the  south  end  by  McClintock  Channel.  It  is 
about  five  hundred  miles  north  of  the  northwest  part 
of  Hudson  Bay.  There  is  a  corresponding  magnetic 
pole  in  the  Antarctic  Ocean,  or  rather  on  Victoria 
Land,  nearly  south  of  Australia.  Its  position  has 
not  been  so  exactly  located  as  in  the  north,  but  it 
is  supposed  to  be  at  about  74°  of  south  latitude  and 
147°  of  east  longitude  from  Greenwich. 

The  magnetic  poles  used  to  be  looked  upon  as  the 
points  towards  which  the  respective  ends  of  the  needle 
were  attracted.  And,  as  a  matter  of  fact,  the  mag- 
netic force  is  stronger  near  the  poles  than  elsewhere. 


SIDE-LIGHTS    ON    ASTRONOMY 

When  located  in  this  way  by  strength  of  force,  it 
is  found  that  there  is  a  second  north  pole  in  northern 
Siberia.  Its  location  has  not,  however,  been  so  well 
determined  as  in  the  case  of  the  American  pole,  and 


DIP   OP  THE   MAGNETIC    NEEDLE    IN    VARIOUS    LATITUDES 

The  arrow-points  show  the  direction  of  the  north  end  of  the  magnetic  needle,  which  dips 
downward  in  north  latitudes,  while  the  south  end  dips  in  south  latitudes 


it  is  not  yet  satisfactorily  shown  that  there  is  any  one 
point  in  Siberia  where  the  direction  of  the  force  is 
exactly  downward. 

The  declination  and  dip,  taken  together,  show  the 
exact  direction  of  the  magnetic  force  at  any  place. 
But  in  order  to  complete  the  statement  of  the  force, 
one  more  element  must  be  given — its  amount.  The 
intensity  of  the  magnetic  force  is  determined  by  sus- 
pending a  magnet  in  a  horizontal  position,  and  then 
allowing  it  to  oscillate  back  and  forth  around  the 
suspension.  The  stronger  the  force,  the  less  the  time 

148 


THE    MARINER'S    COMPASS 

it  will  take  to  oscillate.  Thus,  by  carrying  a  mag- 
net to  various  parts  of  the  world,  the  magnetic  force 
can  be  determined  at  every  point  where  a  proper 
support  for  the  magnet  is  obtainable.  The  intensity 
thus  found  is  called  the  horizontal  force.  This  is  not 
really  the  total  force,  because  the  latter  depends  upon 
the  dip ;  the  greater  the  dip,  the  less  will  be  the  hori- 
zontal force  which  corresponds  to  a  certain  total  force. 
But  a  very  simple  computation  enables  the  one  to  be 
determined  when  the  value  of  the  other  is  known. 
In  this  way  it  is  found  that,  as  a  general  rule,  the 
magnetic  force  is  least  in  the  earth's  equatorial  regions 
and  increases  as  we  approach  either  of  the  magnetic 
poles. 

When  the  most  exact  observations  on  the  direction 
of  the  needle  are  made,  it  is  found  that  it  never  re- 
mains at  rest.  Beginning  with  the  changes  of  short- 
est duration,  we  have  a  change  which  takes  place 
every  day,  and  is  therefore  called  diurnal.  In  our 
-northern  latitudes  it  is  found  that  during  the  six 
hours  from  nine  o'clock  at  night  until  three  in  the 
morning  the  direction  of  the  magnet  remains  nearly 
the  same.  But  between  three  and  four  A.M.  it  be- 
gins to  deviate  towards  the  east,  going  farther  and 
farther  east  until  about  8  A.M.  Then,  rather  sud- 
denly, it  begins  to  swing  towards  the  west  with  a 
much  more  rapid  movement,  which  comes  to  an  end 
between  one  and  two  o'clock  in  the  afternoon.  Then, 
more  slowly,  it  returns  in  an  easterly  direction  until 
about  nine  at  night,  when  it  becomes  once  more  nearly 
quiescent.  Happily,  the  amount  of  this  change  is  so 
small  that  the  navigator  need  not  trouble  himself 
with  it.  The  entire  range  of  movement  rarely  amounts 
to  one-quarter  of  a  degree. 

149 


SIDE-LIGHTS    ON    ASTRONOMY 

It  is  a  curious  fact  that  the  amount  of  the  change 
is  twice  as  great  in  June  as  it  is  in  December.  This 
indicates  that  it  is  caused  by  the  sun's  radiation. 
But  how  or  why  this  cause  should  produce  such  an 
effect  no  one  has  yet  discovered. 

Another  curious  feature  is  that  in  the  southern 
hemisphere  the  direction  of  the  motion  is  reversed, 
although  its  general  character  remains  the  same. 
The  pointing  deviates  towards  the  west  in  the  morn- 
ing, then  rapidly  moves  towards  the  east  until  about 
two  o'clock,  after  which  it  slowly  returns  to  its 
original  direction. 

The  dip  of  the  needle  goes  through  a  similar  cycle 
of  daily  changes.  In  northern  latitudes  it  is  found 
that  at  about  six  in  the  morning  the  dip  begins  to 
increase,  and  continues  to  do  so  until  noon,  after 
which  it* diminishes  until  seven  or  eight  o'clock  in 
the  evening,  when  it  becomes  nearly  constant  for  the 
rest  of  the  night.  In  the  southern  hemisphere  the 
direction  of  the  movement  s  reversed. 

When  the  pointing  of  the  needle  is  compared  with 
the  direction  of  the  moon,  it  is  found  that  there  is  a 
similar  change.  But,  instead  of  following  the  moon 
in  its  course,  it  goes  through  two  periods  in  a  day, 
like  the  tides.  When  the  moon  is  on  the  meridian, 
whether  above  or  below  us,  the  effect  is  in  one  direc- 
tion, while  when  it  is  rising  or  setting  it  is  in  the  op- 
posite direction.  In  other  words,  there  is  a  com- 
plete swinging  backward  and  forward  twice  in  a  lunar 
day.  It  might  be  supposed  that  such  an  effect  would 
be  due  to  the  moon,  like  the  earth,  being  a  magnet. 
But  were  this  the  case  there  would  be  only  one  swing 
back  and  forth  during  the  passage  of  the  moon  from 
the  meridian  until  it  came  back  to  the  meridian  again. 

150 


THE    MARINER'S    COMPASS 

The  effect  would  be  opposite  at  the  rising  and  setting 
of  the  moon,  which  we  have  seen  is  not  the  case.  To 
make  the  explanation  yet  more  difficult,  it  is  found 
that,  as  in  the  case  of  the  sun,  the  change  is  opposite 
in  the  northern  and  southern  hemispheres  and  very 
small  at  the  equator,  where,  by  virtue  of  any  action 
that  we  can  conceive  of,  it  ought  to  be  greatest.  The 
pointing  is  also  found  to  change  with  the  age  of  the 
moon  and  with  the  season  of  the  year.  But  these 
motions  are  too  small  to  be  set  forth  in  the  present 
article. 

There  is  yet  another  class  of  changes  much  wider 
than  these.  The  observations  recorded  since  the 
time  of  Columbus  show  that,  in  the  course  of  cen- 
turies, the  variation  of  the  compass,  at  any  one  point, 
changes  very  widely.  It  is  well  known  that  in  1490 
the  needle  pointed  east  of  north  in  the  Mediterranean, 
as  well  as  in  those  portions  of  the  Atlantic  which  were 
then  navigated.  Columbus  was  therefore  much  as- 
tonished when,  on  his  first  voyage,  in  mid-ocean,  he 
found  that  the  deviation  was  reversed,  and  was  now 
towards  the  west.  It  follows  that  a  line  of  no  varia- 
tion then  passed  through  the  Atlantic  Ocean.  But 
this  line  has  since  been  moving  towards  the  east. 
About  1662  it  passed  the  meridian  of  Paris.  During 
the  two  hundred  and  forty  years  which  have  since 
elapsed,  it  has  passed  over  Central  Europe,  and  now, 
as  we  have  already  said,  passes  through  European 
Russia. 

The  existence  of  natural  magnets  composed  of  iron 
ore,  and  their  property  of  attracting  iron  and  making 
it  magnetic,  have  been  known  from  the  remotest  an- 
tiquity. But  the  question  as  to  who  first  discovered 
the  fact  that  a  magnetized  needle  points  north  and 


SIDE-LIGHTS    ON    ASTRONOMY 

south,  and  applied  this  discovery  to  navigation,  has 
given  rise  to  much  discussion.  That  the  property 
was  known  to  the  Chinese  about  the  beginning  of  our 
era  seems  to  be  fairly  well  established,  the  statements 
to  that  effect  being  of  a  kind  that  could  not  well  have 
been  invented.  Historical  evidence  of  the  use  of  the 
magnetic  needle  in  navigation  dates  from  the  twelfth 
century.  The  earliest  compass  consisted  simply  of 
a  splinter  of  wood  or  a  piece  of  straw  to  which  the 
magnetized  needle  was  attached,  and  which  was 
floated  in  water.  A  curious  obstacle  is  said  to  have 
interfered  with  the  first  uses  of  this  instrument. 
Jack  is  a  superstitious  fellow,  and  we  may  be  sure 
that  he  was  not  less  so  in  former  times  than  he  is  to- 
day. From  his  point  of  view  there  was  something 
uncanny  in  so  very  simple  a  contrivance  as  a  floating 
straw  persistently  showing  him  the  direction  in  which 
he  must  sail.  It  made  him  very  uncomfortable  to  go 
to  sea  under  the  guidance  of  an  invisible  power.  But 
with  him,  as  with  the  rest  of  us,  familiarity  breeds 
contempt,  and  it  did  not  take  more  than  a  generation 
to  show  that  much  good  and  no  harm  came  to  those 
who  used  the  magic  pointer. 

The  modern  compass,  as  made  in  the  most  approved 
form  for  naval  and  other  large  ships,  is  the  liquid  one.  } 
This  does  not  mean  that  the  card  bearing  the  needle 
floats  on  the  liquid,  but  only  that  a  part  of  the  force 
is  taken  off  from  the  pivot  on  which  it  turns,  so  as 
to  make  the  friction  as  small  as  possible,  and  to  pre- 
vent the  oscillation  back  and  forth  which  would  con- . 
tinually  go  on  if  the  card  were  perfectly  free  to  turn. 
The  compass-card  is  marked  not  only  with  the  thirty- 
two  familiar  points  of  the  compass,  but  is  also  divided 
into  degrees.  In  the  most  accurate  navigation  it  is 

152 


THE    MARINER'S    COMPASS 

probable  that  very  little  use  of  the  points  is  made, 
the  ship  being  directed  according  to  the  degrees. 

A  single  needle  is  not  relied  upon  to  secure  the  di- 
rection of  the  card,  the  latter  being  attached  to  a 
system  of  four  or  even  more  magnets,  all  pointing  in 
the  same  direct  on.  The  compass  must  have  no 
iron  in  its  construction  or  support,  because  the  at- 
traction of  that  substance  on  the  needle  would  be 
fatal  to  its  performance.  I 

From  this  cause  the  use  of  iron  as  ship-building 
material  introduced  a  difficulty  which  it  was  feared 
would  prove  very  serious.  The  thousands  of  tons  of 
iron  in  a  ship  must  exert  a  strong  attraction  on  the 
magnetic  needle.  Another  complication  is  introduced 
by  the  fact  that  the  iron  of  the  ship  will  always  be- 
come more  or  less  magnetic,  and  when  the  ship  is 
built  of  steel,  as  modern  ones  are,  this  magnetism  will 
be  more  or  less  permanent. 

We  have  already  said  that  a  magnet  has  the  prop- 
erty of  making  steel  or  iron  in  its  neighborhood  into 
another  magnet,  with  its  poles  pointing  in  the  op- 
posite direction.  The  consequence  is  that  the  mag- 
netism of  the  earth  itself  will  make  iron  or  steel  more 
or  less  magnetic.  As  a  ship  is  built  she  thus  becomes 
a  great  repository  of  magnetism,  the  direction  of  the 
force  of  which  will  depend  upon  the  position  in  which 
she  lay  while  building.  If  erected  on  the  bank  of  an 
east  and  west  stream,  the  north  end  of  the  ship  will 
become  the  north  pole  of  a  magnet  and  the  south  end 
the  south  pole.  Accordingly,  when  she  is  launched 
and  proceeds  to  sea,  the  compass  points  not  exactly 
according  to  the  magnetism  of  the  earth,  but  partly 
according  to  that  of  the  ship  also. 

The  methods  of  obviating  this  difficulty  have  ex- 


SIDE-LIGHTS    ON    ASTRONOMY 

ercised  the  ingenuity  of  the  ablest  physicists  from 
the  beginning  of  iron  ship  building.  One  method  is 
to  place  in  the  neighborhood  of  the  compass,  but  not 
too  near  it,  a  steel  bar  magnetized  in  the  opposite 
direction  from  that  of  the  ship,  so  that  the  action  of 
the  latter  shall  be  neutralized.  But  a  perfect  neu- 
tralization cannot  be  thus  effected.  It  is  all  the 
more  difficult  to  effect  it  because  the  magnetism  of  a 
ship  is  liable  to  change. 

The  practical  method  therefore  adopted  is  called 
"swinging  the  ship,"  an  operation  which  passengers 
on  ocean  liners  may  have  frequently  noticed  when 
approaching  land.  The  ship  is  swung  around  so 
that  her  bow  shall  point  in  various  directions.  At 
each  pointing  the  direction  of  the  ship  is  noticed  by 
sighting  on  the  sun,  and  also  the  direction  of  the 
compass  itself.  In  this  way  the  error  of  the  point- 
ing of  the  compass  as  the  ship  swings  around  is  found 
for  every  direction  in  which  she  may  be  sailing.  A 
table  can  then  be  made  showing  what  the  pointing, 
according  to  the  compass,  should  be  in  order  that 
the  ship  may  sail  in  any  given  direction. 

This,  however,  does  not  wholly  avoid  the  danger. 
The  tables  thus  made  are  good  when  the  ship  is  on  a 
level  keel.  If,  from  any  cause  whatever,  she  heels 
over  to  one  side,  the  action  will  be  different.  Thus 
there  is  a  "heeling  error"  which  must  be  allowed  for. 
It  is  supposed  to  have  been  from  this  source  of 
error  not  having  been  sufficiently  determined  or  ap- 
preciated that  the  lamentable  wreck  of  the  United 
States  ship  Huron  off  the  coast  of  Hatteras  occurred 
some  twenty  years  ago. 


X 

THE    FAIRYLAND    OF    GEOMETRY 

IF  the  reader  were  asked  in  what  branch  of  science 
the  imagination  is  confined  within  the  strictest 
limits,  he  would,  I  fancy,  reply  that  it  must  be  that 
of  mathematics.  The  pursuer  of  this  science  deals 
only  with  problems  requiring  the  most  exact  state- 
ments and  the  most  rigorous  reasoning.  In  all  other 
fields  of  thought  more  or  less  room  for  play  may  be 
allowed  to  the  imagination,  but  here  it  is  fettered  by 
iron  rules,  expressed  in  the  most  rigid  logical  form, 
from  which  no  deviation  can  be  allowed.  We  are 
told  by  philosophers  that  absolute  certainty  is  unat- 
tainable in  all  ordinary  human  affairs,  the  only  field 
in  which  it  is  reached  being  that  of  geometric  demon- 
stration. 

And  yet  geometry  itself  has  its  fairyland — a  land 
in  which  the  imagination,  while  adhering  to  the  forms 
of  the  strictest  demonstration,  roams  farther  than  it 
ever  did  in  the  dreams  of  Grimm  or  Andersen.  One 
thing  which  gives  this  field  its  strictly  mathematical 
character  is  that  it  was  discovered  and  explored  in 
the  search  after  something  to  supply  an  actual  want 
of  mathematical  science,  and  was  incited  by  this 
want  rather  than  by  any  desire  to  give  play  to  fancy. 
Geometricians  have  always  sought  to  found  their 
science  on  the  most  logical  basis  possible,  and  thus 

'55 


SIDE-LIGHTS    ON    ASTRONOMY 

have  carefully  and  critically  inquired  into  its  founda- 
tions. The  new  geometry  which  has  thus  arisen  is 
of  two  closely  related  yet  distinct  forms.  One  of 
these  is  called  non-Euclidian,  because  Euclid's  axiom 
of  parallels,  which  we  shall  presently  explain,  is  ig- 
nored. In  the  other  form  space  is  assumed  to  have 
one  or  more  dimensions  in  addition  to  the  three  to 
which  the  space  we  actually  inhabit  is  confined. 
As  we  go  beyond  the  limits  set  by  Euclid  in  adding 
a  fourth  dimension  to  space,  this  last  branch  as  well 
as  the  other  is  often  designated  non- Euclidian.  But 
the  more  common  term  is  hypergeometry,  which, 
though  belonging  more  especially  to  space  of  more 
than  three  dimensions,  is  also  sometimes  applied  to 
any  geometric  system  which  transcends  our  ordinary 
ideas. 

In  all  geometric  reasoning  some  propositions  are 
necessarily  taken  for  granted.  These  are  called  ax- 
ioms, and  are  commonly  regarded  as  self-evident. 
Yet  their  vital  principle  is  not  so  much  that  of  being 
self-evident  as  being,  from  the  nature  of  the  case, 
incapable  of  demonstration.  Our  edifice  must  have 
some  support  to  rest  upon,  and  we  take  these  axioms 
as  its  foundation.  One  example  of  such  a  geometric 
axiom  is  that  only  one  straight  line  can  be  drawn 
between  two  fixed  points ;  in  other  words,  two  straight 
lines  can  never  intersect  in  more  than  a  single  point. 
The  axiom  with  which  we  are  at  present  concerned 
is  commonly  known  as  the  nth  of  Euclid,  and  may 
be  set  forth  in  the  following  way:  We  have  given  a 
straight  line,  A  B,  and  a  point,  P,  with  another  line, 
C  D,  passing  through  it  and  capable  of  being  turned 
around  on  P.  Euclid  assumes  that  this  line  C  D 
will  have  one  position  in  which  it  will  be  parallel  to 

156 


THE  FAIRYLAND  OF  GEOMETRY 

A  B,  that  is,  a  position  such  that  if  the  two  lines 
are  produced  without  end,  they  will  never  meet. 
His  axiom  is  that  only  one  such  line  can  be  drawn 
through  P.  That  is  to  say,  if  we  make  the  slightest 
possible  change  in  the  direction  of  the  line  C  D,  it 
will  intersect  the  other  line,  either  in  one  direction 
or  the  other. 

The  new  geometry  grew  out  of  the  feeling  that 
this  proposition  ought  to  be  proved 

rather  than  taken  as  an  axiom;  in      c * p 

fact,  that  it  could  in  some  way  be       

derived    from    the    other    axioms. 

Many  demonstrations  of  it  were  at-  FIG-  * 

tempted,  but  it  was  always  found, 

on  critical  examination,  that  the  proposition  itself, 

or  its  equivalent,  had  slyly  worked  itself  in  as  part 

of  the  base  of  the  reasoning,  so  that  the  very  thing 

to  be  proved  was  really  taken  for  granted. 

This  suggested  another  course  of  inquiry.  If  this 
axiom  of  parallels  does  not  follow  from  the  other 
axioms,  then  from  these  latter  we  may  construct  a 
system  of  geometry  in  which  the  axiom  of  parallels 
shall  not  be  true.  This  was  done  by  Lobatchewsky 
and  Bolyai,  the  one  a  Russian  the  other  a  Hungarian 
geometer,  about  1830. 

To  show  how  a  result  which  looks  absurd,  and  is 
really  inconceivable  by  us,  can  be  treated  as  possible 
in  geometry,  we  must  have  recourse  to  analogy. 
Suppose  a  world  consisting  of  a  boundless  flat  plane 
to  be  inhabited  by  reasoning  beings  who  can  move 
about  at  pleasure  on  the  plane,  but  are  not  able  to 
turn  their  heads  up  or  down,  or  even  to  see  or  think 
of  such  terms  as  above  them  and  below  them,  and 
things  around  them  can  be  pushed  or  pulled  about 


SIDE-LIGHTS    ON    ASTRONOMY 

in  any  direction,  but  cannot  be  lifted  up.  People 
and  things  can  pass  around  each  other,  but  cannot 
step  over  anything.  These  dwellers  in  "flatland" 
could  construct  a  plane  geometry  which  would  be 
exactly  like  ours  in  being  based  on  the  axioms  of 
Euclid.  Two  parallel  straight  lines  would  never  meet, 
though  continued  indefinitely. 

But  suppose  that  the  surface  on  which  these  beings 
live,  instead  of  being  an  infinitely  extended  plane,  is 
really  the  surface  of  an  immense  globe,  like  the  earth 
on  which  we  live.  It  needs  no  knowledge  of  geom- 
etry, but  only  an  examination  of  any  globular  object 
— an  apple,  for  example — to  show  that  if  we  draw 
a  line  as  straight  as  possible  on  a  sphere,  and  parallel 
to  it  draw  a  small  piece  of  a  second  line,  and  continue 
this  in  as  straight  a  line  as  we  can,  the  two  lines  will 
meet  when  we  proceed  in  either  direction  one-quarter 
of  the  way  around  the  sphere.  For  our  "flat-land" 
people  these  lines  would  both  be  perfectly  straight, 
because  the  only  curvature  would  be  in  the  direction 
downward,  which  they  could  never  either  perceive 
or  discover.  The  lines  would  also  correspond  to  the 
definition  of  straight  lines,  because  any  portion  of 
either  contained  between  two  of  its  points  would  be 
the  shortest  distance  between  those  points.  And 
yet,  if  these  people  should  extend  their  measures  far 
enough,  they  would  find  any  two  parallel  lines  to  meet 
in  two  points  in  opposite  directions.  For  all  small  - 
spaces  the  axioms  of  their  geometry  would  apparently 
hold  good,  but  when  they  came  to  spaces  as  immense 
as  the  semi-diameter  of  the  earth,  they  would  find 
the  seemingly  absurd  result  that  two  parallel  lines 
woul$,  in  the  course  of  thousands  of  miles,  come  to- 
gether. Another  result  yet  more  astonishing  would 

158 


THE    FAIRYLAND    OF    GEOMETRY 

be  that,  going  ahead  far  enough  in  a  straight  line, 
they  would  find  that  although  they  had  been  going 
forward  all  the  time  in  what  seemed  to  them  the  same 
direction,  they  would  at  the  end  of  25,000  miles  find 
themselves  once  more  at  their  starting-point. 

One  form  of  the  modern  non-Euclidian  geometry 
assumes  that  a  similar  theorem  is  true  for  the  space 
in  which  our  universe  is  contained.  Although  two 
straight  lines,  when  continued  indefinitely,  do  not 
appear  to  converge  even  at  the  immense  distances 
which  separate  us  from  the  fixed  stars,  it  is  possible 
that  there  may  be  a  point  at  which  they  would  event- 
ually meet  without  either  line  having  deviated  from 
its  primitive  direction  as  we  understand  the  case.  It 
would  follow  that,  if  we  could  start  out  from  the 
earth  and  fly  through  space  in  a  perfectly  straight 
line  with  a  velocity  perhaps  millions  of  times  that  of 
light,  we  might  at  length  find  ourselves  approaching 
the  earth  from  a  direction  the  opposite  of  that  in 
which  we  started.  Our  straight-line  circle  would  be 
complete. 

Another  result  of  the  theory  is  that,  if  it  be  true, 
space,  though  still  unbounded,  is  not  infinite,  just  as 
the  surface  of  a  sphere,  though  without  any  edge  or 
boundary,  has  only  a  limited  extent  of  surface.  Space 
would  then  have  only  a  certain  volume — a  volume 
which,  though  perhaps  greater  than  that  of  all  the 
atoms  in  the  material  universe,  would  still  be  capable 
of  being  expressed  in  cubic  miles.  If  we  imagine  our 
earth  to  grow  larger  and  larger  in  every  direction 
without  limit,  and  with  a  speed  similar  to  that  we 
have  described,  so  that  to-morrow  it  was  large  enough 
to  extend  to  the  nearest  fixed  stars,  the  day  after  to 
yet  farther  stars,  and  so  on,  and  we,  living  upon  it, 


SIDE-LIGHTS    ON    ASTRONOMY 

looked  out  for  the  result,  we  should,  in  time,  see  the 
other  side  of  the  earth  above  us,  coming  down  upon 
us,  as  it  were.  The  space  intervening  would  grow 
smaller,  at  last  being  filled  up.  The  earth  would  then 
be  so  expanded  as  to  fill  all  existing  space. 

This,  although  to  us  the  most  interesting  form  of 
the  non-Euclidian  geometry,  is  not  the  only  one. 
The  idea  which  Lobatchewsky  worked  out  was  that 
through  a  point  more  than  one  parallel  to  a  given 
line  could  be  drawn;  that  is  to  say,  if  through  the 
point  P  we  have  already  supposed  another  line  were 
drawn  making  ever  so  small  an  angle  with  C  D,  this 
line  also  would  never  meet  the  line  A  B.  It  might 
approach  the  latter  at  first,  but  would  eventually  di- 
verge. The  two  lines  A  B  and  C  D,  starting  parallel, 
would  eventually,  perhaps  at  distances  greater  than 
that  of  the  fixed  stars,  gradually  diverge  from  each 
other.  This  system  does  not  admit  of  being  shown 
by  analogy  so  easily  as  the  other,  but  an  idea  of  it 
may  be  had  by  supposing  that  the  surface  of  "flat- 
land,"  instead  of  being  spherical,  is  saddle-shaped. 
Apparently  straight  parallel  lines  drawn  upon  it 
would  then  diverge,  as  supposed  by  Bolyai.  We 
cannot,  however,  imagine  such  a  surface  extended 
indefinitely  without  losing  its  properties.  The  anal- 
ogy is  not  so  clearly  marked  as  in  the  other  case. 

To  explain  hypergeometry  proper  we  must  first 
set  forth  what  a  fourth  dimension  of  space  means, 
and  show  how  natural  the  way  is  by  which  it  may  be 
approached.  We  continue  our  analogy  from  "  flat- 
land."  In  this  supposed  land  let  us  make  a  cross- 
two  straight  lines  intersecting  at  right  angles.  The 
inhabitants  of  this  land  understand  the  cross  perfect- 
ly, and  conceive  of  it  just  as  we  do.  But  let  us  ask 

1 60 


THE    FAIRYLAND    OF    GEOMETRY 

them  to  draw  a  third  line,  intersecting  in  the  same 
point,   and   perpendicular  to  both  the   other  lines. 
They  would  at  once  pronounce  this  absurd  and  im- 
possible.     It   is    equally   absurd    and 
impossible    to    us    if  we    require   the 
third  line  to  be  drawn  on  the  paper* 

But  we   should  reply,  "  If  you  allow     , IN- 

us  to  leave  the  paper  or  flat  surface, 

then  we  can    solve   the  problem  by 

simply  drawing  the  third  line  through 

the   paper   perpendicular  to    its    sur-  FIG.  2 

face." 

Now,  to  pursue  the  analogy,  suppose  that,  after 
we  have  drawn  three  mutually  perpendicular  lines, 
some  being  from  another  sphere  proposes  to  us  the 
drawing  of  a  fourth  line  through  the  same  point,  per- 
pendicular to  all  three  of  the  lines  already  there. 
We  should  answer  him  in  the  same  way  that  the  in- 
habitants of  "flat-land"  answered  us:  "The  problem 
is  impossible.  You  cannot  draw  any  such  line  in 
space  as  we  understand  it."  If  our  visitor  conceived 
of  the  fourth  dimension,  he  would  reply  to  us  as  we 
replied  to  the  "flat-land"  people:  "The  problem  is 
absurd  and  impossible  if  you  confine  your  line  to 
space  as  you  understand  it.  But  for  me  there  is  a 
fourth  dimension  in  space.  Draw  your  line  through 
that  dimension,  and  the  problem  will  be  solved. 
This  is  perfectly  simple  to  me ;  it  is  impossible  to  you 
solely  because  your  conceptions  do  not  admit  of 
more  than  three  dimensions." 

Supposing  the  inhabitants  of  "flat -land"  to  be 
intellectual  beings  as  we  are,  it  would  be  interesting 
to  them  to  be  told  what  dwellers  of  space  in  three 
dimensions  could  do.  Let  us  pursue  the  analogy  by 

161 


SIDE-LIGHTS    ON    ASTRONOMY 

showing  what  dwellers  in  four  dimensions  might  do. 
Place  a  dweller  of  "flat-land"  inside  a  circle  drawn 
on  his  plane,  and  ask  him  to  step  outside  of  it  with- 
out breaking  through  it.  He  would  go  all  around, 
and,  finding  every  inch  of  it  closed,  he  would  say  it 
was  impossible  from  the  very  nature  of  the  conditions. 
" But,"  we  would  reply,  "that  is  because  of  your  lim- 
ited conceptions.  We  can  step  over  it." 

"Step  over  it!"  he  would  exclaim.  "I  do  not 
know  what  that  means.  I  can  pass  around  anything 
if  there  is  a  way  open,  but  I  cannot  imagine  what  you 
mean  by  stepping  over  it." 

But  we  should  simply  step  over  the  line  and  reap- 
pear on  the  other  side.  So,  if  we  confine  a  being  able 
to  move  in  a  fourth  dimension  in  the  walls  of  a  dun- 
geon of  which  the  sides,  the  floor,  and  the  ceiling 
were  all  impenetrable,  he  would  step  outside  of  it 
without  touching  any  part  of  the  building,  just  as 
easily  as  we  could  step  over  a  circle  drawn  on  the 
plane  without  touching  it.  He  would  simply  disap- 
pear from  our  view  like  a  spirit,  and  perhaps  re- 
appear the  next  moment  outside  the  prison.  To 
do  this  he  would  only  have  to  make  a  little  excur- 
sion in  the  fourth  dimension. 

Another  curious  application  of  the  principle  is  more 

purely  geometrical. 

We  have  here  two 

triangles,  of  which 
FIG.  3  the  sides  and  angles 

of  the  one  are  all 

equal  to  corresponding  sides  and  angles  of  the  other. 
Euclid  takes  it  for  granted  that  the  one  triangle  can 
be  laid  upon  the  other  so  that  the  two  shall  fit  to- 
gether. But  this  cannot  be  done  unless  we  lift  one 

162 


kTHE    FAIRYLAND    OF    GEOMETRY 
and  turn  it  over.     In  the  geometry  of  "flat-land" 
h  a  thing  as  lifting  up  is  inconceivable;  the  two 
triangles  could  never  be  fitted  together. 

Now  let  us  suppose  two  pyramids  similarly  related. 
All  the  faces  and  angles  of  the  one  correspond  to  the 
faces  and  angles  of  the  other.  Yet,  lift  them  about 


FIG.  4 

as  we  please,  we  could  never  fit  them  together.  If 
we  fit  the  bases  together  the  two  will  lie  on  opposite 
sides,  one  being  below  the  other.  But  the  dweller  in 
four  dimensions  of  space  will  fit  them  together  with- 
out any  trouble.  By  the  mere  turning  over  of  one 
he  will  convert  it  into  the  other  without  any  change 
whatever  in  the  relative  position  of  its  parts.  What 
he  could  do  with  the  pyramids  he  could  also  do  with 
one  of  us  if  we  allowed  him  to  take  hold  of  us  and  turn 
a  somersault  with  us  in  the  fourth  dimension.  We 
should  then  come  back  into  our  natural  space,  but 
changed  as  if  we  were  seen  in  a  mirror.  Everything 
on  us  would  be  changed  from  right  to  left,  even  the 
seams  in  our  clothes,  and  every  hair  on  our  head. 
All  this  would  be  done  without,  during  any  of  the 
motion,  any  change  having  occurred  in  the  positions 
of  the  parts  of  the  body. 

It   is  very  curious  that,  in   these   transcendental 
speculations,  the  most  rigorous  mathematical  meth- 

163 


SIDE-LIGHTS    ON    ASTRONOMY 

ods  correspond  to  the  most  mystical  ideas  of  the 
Swedenborgian  and  other  forms  of  religion.  Right 
around  us,  but  in  a  direction  which  we  cannot  con- 
ceive any  more  than  the  inhabitants  of  "flat-land" 
can  conceive  up  and  down,  there  may  exist  not  mere- 
ly another  universe,  but  any  number  of  universes. 
All  that  physical  science  can  say  a'gainst  the  supposi- 
tion is  that,  even  if  a  fourth  dimension  exists,  there 
is  some  law  of  all  the  matter  with  which  we  are  ac- 
quainted which  prevents  any  of  it  from  entering  that 
dimension,  so  that,  in  our  natural  condition,  it  must 
forever  remain  unknown  to  us. 

Another  possibility  in  space  of  four  dimensions 
would  be  that  of  turning  a  hollow  sphere,  an  india- 
rubber  ball,  for  example,  inside  out  by  simple  bending 
without  tearing  it.  To  show  the  motion  in  our  space 
to  which  this  is  analogous,  let  us  take  a  thin,  round 
sheet  of  india  -  rubber,  and  cut  out  all  the  central 
part,  leaving  only  a  narrow  ring  round  the  border. 
Suppose  the  outer  edge  of  this  ring  fastened  down 
on  a  table,  while  we  take  hold  of  the  inner  edge  and 
stretch  it  upward  and  outward  over  the  outer  edge 
until  we  flatten  the  whole  ring  on  the  table,  upside 
down,  with  the  inner  edge  now  the  outer  one.  This 
motion  would  be  as  inconceivable  in  "flat-land"  as 
turning  the  ball  inside  out  is  to  us. 


XI 

THE  ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

THE  claims  of  scientific  research  on  the  public 
were  never  more  forcibly  urged  than  in  Professor 
Ray  Lankester's  recent  Romanes  Lecture  before  the 
University  of  Oxford.  Man  is  here  eloquently  pict- 
ured as  Nature's  rebel,  who,  under  conditions  where 
his  great  superior  commands  "Thou  shalt  die,"  re- 
plies "I  will  live."  In  pursuance  of  this  determina- 
tion, civilized  man  has  proceeded  so  far  in  his  inter- 
ference with  the  regular  course  of  Nature  that  he 
must  either  go  on  and  acquire  firmer  control  of  the 
conditions,  or  perish  miserably  by  the  vengeance 
certain  to  be  inflicted  on  the  half-hearted  meddler  in 
great  affairs.  This  rebel  by  every  step  forward  ren- 
ders himself  liable  to  greater  and  greater  penalties, 
and  so  cannot  afford  to  pause  or  fail  in  one  single 
step.  One  of  Nature's  most  powerful  agencies  in 
thwarting  his  determination  to  live  is  found  in  disease- 
producing  parasites.  "Where  there  is  one  man  of 
first-rate  intelligence  now  employed  in  gaining  knowl- 
edge of  this  agency,  there  should  be  a  thousand.  It 
should  be  as  much  the  purpose  of  civilized  nations 
to  protect  their  citizens  in  this  respect  as  it  is  to  pro- 
vide defence  against  human  aggression." 

It  was  no  part  of  the  function  of  the  lecturer  to 
devise  a  plan  for  carrying  on  the  great  war  he  pro- 

165 


SIDE-LIGHTS    ON    ASTRONOMY 

poses  to  wage.  The  object  of  the  present  article  is 
to  contribute  some  suggestions  in  this  direction; 
with  especial  reference  to  conditions  in  our  own  coun- 
try ;  and  no  better  text  can  be  found  for  a  discourse 
on  the  subject  than  the  preceding  quotation.  In 
saying  that  there  should  be  a  thousand  investigators 
of  disease  where  there  is  now  one,  I  believe  that  Pro- 
fessor Lankester  would  be  the  first  to  admit  that  this 
statement  was  that  of  an  ideal  to  be  aimed  at,  rather 
than  of  an  end  to  be  practically  reached.  Every 
careful  thinker  will  agree  that  to  gather  a  body  of 
men, . young  or  old,  supply  them  with  laboratories 
and  microscopes,  and  tell  them  to  investigate  disease, 
would  be  much  like  sending  out  an  army  without 
trained  leaders  to  invade  an  enemy's  country. 

There  is  at  least  one  condition  of  success  in  this 
line  which  is  better  fulfilled  in  our  own  country  than 
in  any  other;  and  that  is  liberality  of  support  on  the 
part  of  munificent  citizens  desirous  of  so  employ- 
ing their  wealth  as  to  promote  the  public  good. 
Combining  this  instrumentality  with  the  general  pub- 
lic spirit  of  our  people,  it  must  be  admitted  that, 
with  all  the  disadvantages  under  which  scientific  re- 
search among  us  has  hitherto  labored,  there  is  still 
no  country  to  which  we  can  look  more  hopefully  than 
to  our  own  as  the  field  in  which  the  ideal  set  forth 
by  Professor  Lankester  is  to  be  pursued.  Some 
thoughts  on  the  question  how  scientific  research  may 
be  most  effectively  promoted  in  our  own  country 
through  organized  effort  may  therefore  be  of  interest. 
Our  first  step  will  be  to  inquire  what  general  lessons 
are  to  be  learned  from  the  experience  of  the  past. 

The  first  and  most  important  of  these  lessons  is 
that  research  has  never  reached  its  highest  develop- 

166 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

ment  except  at  centres  where  bodies  of  men  engaged 
in  it  have  been  brought  together,  and  stimulated  to 
action  by  mutual  sympathy  and  support.  We  must 
call  to  mind  that,  although  the  beginnings  of  modern 
science  were  laid  by  such  men  as  Copernicus,  Galileo, 
Leonardo  da  Vinci,  and  Torricelli,  before  the  middle 
of  the  seventeenth  century,  unbroken  activity  and 
progress  date  from  the  foundations  of  the  Academy 
of  Sciences  of  Paris  and  the  Royal  Society  of  London 
at  that  time.  The  historic  fact  that  the  bringing  of 
men  together,  and  their  support  by  an  intelligent 
and  interested  community,  is  the  first  requirement 
to  be  kept  in  view  can  easily  be  explained.  Effective 
research  involves  so  intricate  a  net-work  of  problems 
and  considerations  that  no  one  engaged  in  it  can  fail 
to  profit  by  the  suggestions  of  kindred  spirits,  even 
if  less  acquanted  with  the  subject  than  he  is  himself. 
Intelligent  discussion  suggests  new  ideas  and  con- 
tinually carries  the  mind  to  a  higher  level  of  thought. 
We  must  not  regard  the  typical  scientific  worker, 
even  of  the  highest  class,  as  one  who,  having  chosen 
his  special  field  and  met  with  success  in  cultivating 
it,  has  only  to  be  supplied  with  the  facilities  he  may 
be  supposed  to  need  in  order  to  continue  his  work  in 
the  most  efficient  way.  What  we  have  to  deal  with 
is  not  a  fixed  and  permanent  body  of  learned  men, 
each  knowing  all  about  the  field  of  work  in  which  he 
is  engaged,  but  a  changing  and  growing  class,  con- 
stantly  recruited  by  beginners  at  the  bottom  of  the 
scale,  and  constantly  depleted  by  the  old  dropping 
away  at  the  top.  No  view  of  the  subject  is  complete 
which  does  not  embrace  the  entire  activity  of  the 
investigator,  from  the  tyro  to  the  leader.  The  leader 
himself,  unless  engaged  in  the  prosecution  of  some 

ia  167 


SIDE-LIGHTS    ON    ASTRONOMY 

narrow  specialty,  can  rarely  be  so  completely  ac- 
quainted with  his  field  as  not  to  need  information 
from  others.  Without  this,  he  is  constantly  liable 
to  be  repeating  what  has  already  been  better  done 
than  he  can  do  it  himself,  of  following  lines  which 
are  known  to  lead  to  no  result,  and  of  adopting 
methods  shown  by  the  experience  of  others  not  to 
be  the  best.  Even  the  books  and  published  re- 
searches to  which  he  must  have  access  may  be  so 
voluminous  that  he  cannot  find  time  to  completely 
examine  them  for  himself ;  or  they  may  be  inaccessi- 
ble. All  this  will  make  it  clear  that,  with  an  occa- 
sional exception,  the  best  results  of  research  are  not 
to  be  expected  except  at  centres  where  large  bodies 
of  men  are  brought  into  close  personal  contact. 

In  addition  to  the  power  and  facility  acquired  by; 
frequent  discussion  with  his  fellows,  the  appreciation 
and  support  of  an  intelligent  community,  to  whom 
the  investigator  may,  from  time  to  time,  make  known 
his  thoughts  and  the  results  of  his  work,  add  a  most 
effective  stimulus.  The  greater  the  number  of  men 
of  like  minds  that  can  be  brought  together  and  the 
larger  the  community  which  interests  itself  in  what 
they  are  doing,  the  more  rapid  will  be  the  advance 
and  the  more  effective  the  work  carried  on.  It  is 
thus  that  London,  with  its  munificently  supported 
institutions,  and  Paris  and  Berlin,  with  their  bodies 
of  investigators  supported  either  by  the  government 
or  by  various  foundations,  have  been  for  more  than 
three  centuries  the  great  centres  where  we  find  scien- 
tific activity  most  active  and  most  effective.  Look- 
ing at  this  undoubted  fact,  which  has  asserted  itself 
through  so  long  a  period,  and  which  asserts  itself  to- 
day more  strongly  than  ever,  the  writer  conceives 

1 68 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

that  there  can  be  no  question  as  to  one  proposition. 
If  we  aim  at  the  single  object  of  promoting  the  ad- 
vance of  knowledge  in  the  most  effective  way,  and 
making  our  own  country  the  leading  one  in  research, 
our  efforts  should  be  directed  towards  bringing  to- 
gether as  many  scientific  workers  as  possible  at  a 
single  centre,  where  they  can  profit  in  the  highest  de- 
gree by  mutual  help,  support,  and  sympathy. 

In  thus  strongly  setting  forth  what  must  seem  an 
indisputable  conclusion,  the  writer  does  not  deny 
that  there  are  drawbacks  to  such  a  policy,  as  there 
are  to  every  policy  that  can  be  devised  aiming  at  a 
good  result.  Nature  offers  to  society  no  good  that 
she  does  not  accompany  by  a  greater  or  less  measure 
of  evil  The  only  question  is  whether  the  good  out- 
weighs the  evil.  In  the  present  case,  the  seeming 
evil,  whether  real  or  not,  is  that  of  centralization. 
A  policy  tending  in  this  direction  is  held  to  be  con- 
trary to  the  best  interests  of  science  in  quarters  en- 
titled to  so  much  respect  that  we  must  inquire  into 
the  soundness  of  the  objection. 

It  would  be  idle  to  discuss  so  extreme  a  question  as 
whether  we  shall  take  all  the  best  scientific  investi- 
gators of  our  country  from  their  several  seats  of 
learning  and  attract  them  to  some  one  point.  We 
know  that  this  cannot  be  done,  even  were  it  granted 
that  success  would  be  productive  of  great  results. 
The  most  that  can  be  done  is  to  choose  some  existing 
centre  of  learning,  population,  wealth,  and  influence, 
and  do  what  we  can  to  foster  the  growth  of  science 
at  that  centre  by  attracting  thither  the  greatest  pos- 
sible number  of  scientific  investigators,  especially  of 
the  younger  class,  and  making  it  possible  for  them 
to  pursue  their  researches  in  the  most  effective  way. 

169 


SIDE-LIGHTS    ON    ASTRONOMY 

This  policy  would  not  result  in  the  slightest  harm 
to  any  institution  or  community  situated  else- 
where. It  would  not  be  even  like  building  up  a 
university  to  outrank  all  the  others  of  our  country; 
because  the  functions  of  the  new  institution,  if  such 
should  be  founded,  would  in  its  relations  to  the  coun- 
try be  radically  different  from  those  of  a  university. 
Its  primary  object  would  not  be  the  education  of 
youth,  but  the  increase  of  knowledge.  So  far  as  the 
interests  of  any  community  or  of  the  world  at  large 
are  concerned,  it  is  quite  indifferent  where  knowledge 
may  be  acquired,  because,  when  once  acquired  and 
made  public,  it  is  free  to  the  world.  The  drawbacks 
suffered  by  other  centres  would  be  no  greater  than 
those  suffered  by  our  Western  cities,  because  all  the 
great  departments  of  the  government  are  situated 
at  a  single  distant  point.  Strong  arguments  could 
doubtless  be  made  for  locating  some  of  these  depart- 
ments in  the  Far  West,  in  the  Mississippi  Valley,  or 
in  various  cities  of  the  Atlantic  coast ;  but  every  one 
knows  that  any  local  advantages  thus  gained  would 
be  of  no  importance  compared  with  the  loss  of  that 
administrative  efficiency  which  is  essential  to  the 
whole  country. 

There  is,  therefore,  no  real  danger  from  centraliza- 
tion. The  actual  danger  is  rather  in  the  opposite  di- 
rection ;  that  the  sentiment  against  concentrating  re- 
search will  prove  to  operate  too  strongly.  There  is  a 
feeling  that  it  is  rather  better  to  leave  every  investi- 
gator where  he  chances  to  be  at  the  moment,  a  feeling 
which  sometimes  finds  expression  in  the  apothegm 
that  we  cannot  transplant  a  genius.  That  such  a  prop- 
osition should  find  acceptance  affords  a  striking  exam- 
ple of  the  readiness  of  men  to  accept  a  euphonious 

170 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

phrase  without  inquiring  whether  the  facts  support  the 
doctrine  which  it  enunciates.  The  fact  is  that  many, 
perhaps  the  majority,  of  the  great  scientific  investiga- 
tors of  this  and  of  former  times  have  done  their  best 
work  through  being  transplanted.  As  soon  as  the  en- 
lightened monarchs  of  Europe  felt  the  importance  of 
making  their  capitals  great  centres  of  learning,  they 
began  to  invite  eminent  men  of  other  countries  to 
their  own.  Lagrange  was  an  Italian  transplanted  to 
Paris,  as  a  member  of  the  Academy  of  Sciences,  after 
he  had  shown  his  powers  in  his  native  country.  His 
great  contemporary,  Euler,  was  a  Swiss,  transplanted 
first  to  St.  Petersburg,  then  invited  by  Frederick  the 
Great  to  become  a  member  of  the  Berlin  Academy, 
then  again  attracted  to  St.  Petersburg.  Huyghens 
was  transplanted  from  his  native  country  to  Paris. 
Agassiz  was  an  exotic,  brought  among  us  from 
Switzerland,  whose  activity  during  the  generation 
he  passed  among  us  was  as  great  and  effective  as  at 
any  time  of  his  life.  On  the  Continent,  outside  of 
France,  the  most  eminent  professors  in  the  univer- 
sities have  been  and  still  are  brought  from  distant 
points.  So  numerous  are  the  cases  of  which  these 
are  examples  that  it  would  be  more  in  accord  with 
the  facts  to  claim  that  it  is  only  by  transplanting  a 
genius  that  we  stimulate  him  to  his  best  work. 

Having  shown  that  the  best  results  can  be  ex- 
pected only  by  bringing  into  contact  as  many  scien- 
tific investigators  as  possible,  the  next  question  which 
arises  is  that  of  their  relations  to  one  another.  It 
may  be  asked  whether  we  shall  aim  at  individualism 
or  collectivism.  Shall  our  ideal  be  an  organized 
system  of  directors,  professors,  associates,  assistants, 
fellows ;  or  shall  it  be  a  collection  of  individual  work- 


SIDE-LIGHTS    ON    ASTRONOMY 

ers,  each  pursuing  his  own  task  in  the  way  he  deems 
best,  untrammelled  by  authority? 

The  reply  to  this  question  is  that  there  is  in  this 
special  case  no  antagonism  between  the  two  ideas. 
The  most  effective  organization  will  aim  both  at  the 
promotion  of  individual  effort,  and  at  subordination 
and  co-operation.  It  would  be  a  serious  error  to 
formulate  any  general  rule  by  which  all  cases  should 
be  governed.  The  experience  of  the  past  should  be 
our  guide,  so  far  as  it  applies  to  present  and  future 
conditions;  but  in  availing  ourselves  of  it  we  must 
remember  that  conditions  are  constantly  changing, 
and  must  adapt  our  policy  to  the  problems  of  the 
future.  In  doing  this,  we  shall  find  that  different 
fields  of  research  require  very  different  policies  as 
regards  co-operation  and  subordination.  It  will  be 
profitable  to  point  out  those  special  differences, 
because  we  shall  thereby  gain  a  more  luminous  in- 
sight into  the  problems  which  now  confront  the 
scientific  investigator,  and  better  appreciate  their 
variety,  and  the  necessity  of  different  methods  of 
dealing  with  them. 

At  one  extreme,  we  have  the  field  of  normative 
science,  work  in  which  is  of  necessity  that  of  the 
individual  mind  alone.  This  embraces  pure  mathe- 
matics and  the  methods  of  science  in  their  widest 
range.  The  common  interests  of  science  require 
that  these  methods  shall  be  worked  out  and  formu- 
lated for  the  guidance  of  investigators  generally,  and 
this  work  is  necessarily  that  of  the  individual  brain. 

At  the  other  extreme,  we  have  the  great  and  grow- 
ing body  of  sciences  of  observation.  Through  the 
whole  nineteenth  century,  to  say  nothing  of  previous 
centuries,  organizations,  and  even  individuals,  have 

172 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

been  engaged  in  recording  the  innumerable  phases 
of  the  course  of  nature,  hoping  to  accumulate  ma- 
terial that  posterity  shall  be  able  to  utilize  for  its 
benefit.  We  have  observations  astronomical,  me- 
teorological, magnetic,  and  social,  accumulating  in 
constantly  increasing  volume,  the  mass  of  which  is 
so  unmanageable  with  our  present  organizations  that 
the  question  might  well  arise  whether  almost  the 
whole  of  it  will  not  have  to  be  consigned  to  oblivion. 
Such  a  conclusion  should  not  be  entertained  until  we 
have  made  a  vigorous  effort  to  find  what  pure  metal 
of  value  can  be  extracted  from  the  mass  of  ore.  To 
do  this  requires  the  co-operation  of  minds  of  various 
orders,  quite  akin  in  their  relations  to  those  neces- 
sary in  a  mine  or  great  manufacturing  establishment. 
Laborers  whose  duties  are  in  a  large  measure  matters 
of  routine  must  be  guided  by  the  skill  of  a  class 
higher  in  quality  and  smaller  in  number  than  their 
own,  and  these  again  by  the  technical  knowledge  of 
leaders  in  research.  Between  these  extremes  we 
have  a  great  variety  of  systems  of  co-operation. 

There  is  another  feature  of  modern  research  the 
apprehension  of  which  is  necessary  to  the  complete- 
ness of  our  view.  A  cursory  survey  of  the  field  of 
science  conveys  the  impression  that  it  embraces  only 
a  constantly  increasing  number  of  disconnected 
specialties,  in  which  each  cultivator  knows  little  or 
nothing  of  what  is  being  done  by  others.  Measured 
by  its  bulk,  the  published  mass  of  scientific  research 
is  increasing  in  a  more  than  geometrical  ratio.  Not 
only  do  the  publications  of  nearly  every  scientific 
society  increase  in  number  and  volume,  but  new 
and  vigorous  societies  are  constantly  organized  to 
add  to  the  sum  total.  The  stately  quartos  issued 


SIDE-LIGHTS    ON    ASTRONOMY 

from  the  presses  of  the  leading  academies  of  Europe 
are,  in  most  cases,  to  be  counted  by  hundreds.  The 
Philosophical  Transactions  of  the  Royal  Society  al- 
ready number  about  two  hundred  volumes,  and  the 
time  when  the  Memoirs  of  the  French  Academy  of 
Sciences  shall  reach  the  thousand  mark  does  not 
belong  to  the  very  remote  future.  Besides  such 
large  volumes,  these  and  other  societies  publish 
smaller  ones  in  a  constantly  growing  number.  In 
addition  to  the  publications  of  learned  societies,  there 
are  journals  devoted  to  each  scientific  specialty, 
which  seem  to  propagate  their  species  by  subdivision 
in  much  the  same  way  as  some  of  the  lower  orders 
of  animal  life.  Every  new  publication  of  the  kind  is 
suggested  by  the  wants  of  a  body  of  specialists,  who 
require  a  new  medium  for  their  researches  and  com- 
munications. The  time  has  already  come  when  we 
cannot  assume  that  any  specialist  is  acquainted  with 
all  that  is  being  done  even  in  his  own  line.  To  keep 
the  run  of  this  may  well  be  beyond  his  own  powers; 
more  he  can  rarely  attempt. 

What  is  the  science  of  the  future  to  do  when  this 
huge  mass  outgrows  the  space  that  can  be  found  for 
it  in  the  libraries,  and  what  are  we  to  say  of  the 
value  of  it  all?  Are  all  these  scientific  researches  to 
be  classed  as  really  valuable  contributions  to  knowl- 
edge, or  have  we  only  a  pile  in  which  nuggets  of 
gold  are  here  and  there  to  be  sought  for?  One  en- 
couraging answer  to  such  a  question  is  that,  taking 
the  interests  of  the  world  as  a  whole,  scientific  in- 
vestigation has  paid  for  itself  in  benefits  to  human- 
ity a  thousand  times  over,  and  that  all  that  is  known 
to-day  is  but  an  insignificant  fraction  of  what  Nature 
has  to  show  us.  Apart  from  this,  another  feature  of 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

the  science  of  our  time  demands  attention.  While 
we  cannot  hope  that  the  multiplication  of  specialties 
will  cease,  we  find  that  upon  the  process  of  differ- 
entiation and  subdivision  is  now  being  superposed  a 
form  of  evolution,  tending  towards  the  general  unity 
of  all  the  sciences,  of  which  some  examples  may  be 
pointed  out. 

Biological  science,  which  a  generation  ago  was 
supposed  to  be  at  the  antipodes  of  exact  science,  is 
becoming  more  and  more  exact,  and  is  cultivated  "by 
methods  which  are  developed  and  taught  by  mathe- 
maticians. Psychophysics — the  study  of  the  opera- 
tions of  the  mind  by  physical  apparatus  of  the  same 
general  nature  as  that  used  by  the  chemist  and 
physicist — is  now  an  established  branch  of  research. 
A  natural  science  which,  if  any  comparisons  are  pos- 
sible, may  outweigh  all  others  in  importance  to  the 
race,  is  the  rising  one  of  "eugenics," — the  improve- 
ment of  the  human  race  by  controlling  the  production 
of  its  offspring.  No  better  example  of  the  drawbacks 
which  our  country  suffers  as  a  seat  of  science  can 
be  given  than  the  fact  that  the  beginning  of  such  a 
science  has  been  possible  only  at  the  seat  of  a  larger 
body  of  cultivated  men  than  our  land  has  yet  been 
able  to  bring  together.  Generations  may  elapse  be- 
fore the  seed  sown  by  Mr.  Francis  Gal  ton,  from  which 
grew  the  Eugenic  Society,  shall  bear  full  fruit  in  the 
adoption  of  those  individual  efforts  and  social  regu- 
lations necessary  to  the  propagation  of  sound  and 
healthy  offspring  on  the  part  of  the  human  family. 
But  when  this  comes  about,  then  indeed  will  Pro- 
fessor Lankester's  "rebel  against  Nature"  find  his 
independence  acknowledged  by  the  hitherto  merci- 
less despot  that  has  decreed  punishment  for  his  treason. 


SIDE-LIGHTS    ON    ASTRONOMY 

This  new  branch  of  science  from  which  so  much 
may  be  expected  is  the  offshoot  of  another,  the  rapid 
growth  of  which  illustrates  the  rapid  invasion  of  the 
most  important  fields  of  thought  by  the  methods  of 
exact  science.  It  is  only  a  few  years  since  it  was 
remarked  of  Professor  Karl  Pearson's  mathematical 
investigations  into  the  laws  of  heredity,  and  the 
biological  questions  associated  with  these  laws,  that 
he  was  working  almost  alone,  because  the  biologists 
did  not  understand  his  mathematics,  while  the  mathe- 
maticians were  not  interested  in  his  biology.  Had 
he  not  lived  at  a  great  centre  of  active  thought, 
within  the  sphere  of  influence  of  the  two  great  uni- 
versities of  England,  it  is  quite  likely  that  this  con- 
dition of  isolation  would  have  been  his  to  the  end. 
But,  one  by  one,  men  were  found  possessing  the  skill 
and  interest  in  the  subject  necessary  to  unite  in  his 
work,  which  now  has  not  only  a  journal  of  its  own, 
but  is  growing  in  a  way  which,  though  slow,  has  all 
the  marks  of  healthy  progress  towards  an  end  the 
importance  of  which  has  scarcely  dawned  upon  the 
public  mind. 

Admitting  that  an  organized  association  of  in- 
vestigators is  of  the  first  necessity  to  secure  the  best 
results  in  the  scientific  work  of  the  future,  we  meet 
the  question  of  the  conditions  and  auspices  under 
which  they  are  to  be  brought  together.  The  first 
thought  to  strike  us  at  this  point  may  well  be  that 
we  have,  in  our  great  universities,  organizations 
which  include  most  of  the  leading  men  now  engaged 
in  scientific  research,  whose  personnel  and  facilities 
we  should  utilize.  Admitting,  as  we  all  do,  that 
there  are  already  too  many  universities,  and  that 
better  work  would  be  done  by  a  consolidation  of  the 

176 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

smaller  ones,  a  natural  conclusion  is  that  the  end 
in  view  will  be  best  reached  through  existing  organiza- 
tions. But  it  would  be  a  great  mistake  to  jump  at 
this  conclusion  without  a  careful  study  of  the  con- 
ditions. The  brief  argument — there  are  already  too 
many  institutions — instead  of  having  more  we  should 
strengthen  those  we  have — should  not  be  accepted 
without  examination.  Had  it  been  accepted  thirty 
years  ago,  there  are  at  least  two  great  American  uni- 
versities of  to-day  which  would  not  have  come  into 
being,  the  means  devoted  to  their  support  having 
been  divided  among  others.  These  are  the  Johns 
Hopkins  and  the  University  of  Chicago.  What  would 
have  been  gained  by  applying  the  argument  in  these 
cases?  The  advantage  would  have  been  that,  in- 
stead of  146  so-called  universities  which  appear  to- 
day in  the  Annual  Report  of  the  Bureau  of  Education, 
we  should  have  had  only  144.  The  work  of  these 
144  would  have  been  strengthened  by  an  addition  to 
their  resources,  represented  by  the  endowments  of 
Baltimore  and  Chicago,  and  sufficient  to  add  per- 
haps one  professor  to  the  staff  of  each.  Would  the 
result  have  been  better  than  it  actually  has  been? 
Have  we  not  gained  anything  by  allowing  the  argu- 
ment to  be  forgotten  in  the  cases  of  these  two  in- 
stitutions? I  do  not  believe  that  any  who  carefully 
look  at  the  subject  will  hesitate  in  answering  this 
question  in  the  affirmative.  The  essential  point  is 
that  the  Johns  Hopkins  University  did  not  merely 
add  one  to  an  already  overcrowded  list,  but  that  it 
undertook  a  mission  which  none  of  the  others  was 
then  adequately  carrying  out.  If  it  did  not  plant 
the  university  idea  in  American  soil,  it  at  least  gave 
it  an  impetus  which  has  now  made  it  the  dom- 

177 


SIDE-LIGHTS    ON    ASTRONOMY 

inant  one  in  the  higher  education  of  almost  every 
state. 

The  question  whether  the  country  at  large  would 
have  reaped  a  greater  benefit,  had  the  professors  of  the 
University  of  Chicago,  with  the  appliances  they  now 
command,  been  distributed  among  fifty  or  a  hundred 
institutions  in  every  quarter  of  the  land,  than  it  has 
actually  reaped  from  that  university,  is  one  which 
answers  itself.  Our  two  youngest  universities  have 
attained  success,  not  because  two  have  thus  been 
added  to  the  number  of  American  institutions  of 
learning,  but  because  they  had  a  special  mission, 
required  by  the  advance  of  the  age,  for  which  exist- 
ing institutions  were  inadequate. 

The  conclusion  to  which  these  considerations  lead 
is  simple.  No  new  institution  is  needed  to  pursue 
work  on  traditional  lines,  guided  by  traditional  ideas. 
But,  if  a  new  idea  is  to  be  vigorously  prosecuted,  then 
a  young  and  vigorous  institution,  specially  organized 
to  put  the  idea  into  effect,  is  necessary.  The  project 
of  building  up  in  our  midst,  at  the  most  appropriate 
point,  an  organization  of  leading  scientific  investi- 
gators, for  the  single  purpose  of  giving  a  new  impetus 
to  American  science  and,  if  possible,  elevating  the 
thought  of  the  country  and  of  the  world  to  a  higher 
plane,  involves  a  new  idea,  which  can  best  be  realized 
by  an  institution  organized  for  the  special  purpose. 
While  this  purpose  is  quite  in  line  with  that  of  the 
leading  universities,  it  goes  too  far  beyond  them  to 
admit  of  its  complete  attainment  through  their  in- 
strumentality. The  first  object  of  a  university  is  the 
training  of  the  growing  individual  for  the  highest 
duties  of  life.  Additions  to  the  mass  of  knowledge 
have  not  been  its  principal  function,  nor  even  an 

178 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

important  function  in  our  own  country,  until  a  recent 
time.  The  primary  object  of  the  proposed  institu- 
tion is  the  advance  of  knowledge  and  the  opening 
up  of  new  lines  of  thought,  which,  it  may  be  hoped, 
are  to  prove  of  great  import  to  humanity.  It  does 
not  follow  that  the  function  of  teaching  shall  be 
wholly  foreign  to  its  activities.  It  must  take  up  the 
best  young  men  at  the  point  where  universities  leave 
them,  and  train  them  in  the  arts  of  thinking  and  in- 
vestigating. But  this  training  will  be  beyond  that 
which  any  regular  university  is  carrying  out. 

In  pursuing  our  theme  the  question  next  arises  as 
to  the  special  features  of  the  proposed  association. 
The  leading  requirement  is  one  that  cannot  be  too 
highly  emphasized.  How  clearly  soever  the  or- 
ganizers may  have  in  their  minds*  eye  the  end  in 
view,  they  must  recognize  the  fact  that  it  cannot  be 
attained  in  a  day.  In  every  branch  of  work  which 
is  undertaken,  there  must  be  a  single  leader,  and  he 
must  be  the  best  that  the  country,  perhaps  even  the 
world,  can  produce.  The  required  man  is  not  to  be 
found  without  careful  inquiry;  in  many  branches  he 
may  be  unattainable  for  years.  When  such  is  the 
case,  wait  patiently  till  he  appears.  Prudence  re- 
quires that  the  fewest  possible  risks  would  be  taken, 
and  that  no  leader  should  be  chosen  except  one  of 
tried  experience  and  world- wide  reputation.  Yet 
we  should  not  leave  wholly  out  of  sight  the  success 
of  the  Johns  Hopkins  University  in  selecting,  at  its 
very  foundation,  young  men  who  were  to  prove 
themselves  the  leaders  of  the  future.  This  experi- 
ence may  admit  of  being  repeated,  if  it  be  carefully 
borne  in  mind  that  young  men  of  promise  are  to  be 
avoided  and  young  men  of  performance  only  to  be 

179 


SIDE-LIGHTS    ON    ASTRONOMY 

considered.  The  performance  need  not  be  striking: 
ex  pede  Herculem  may  be  possible;  but  we  must  be 
sure  of  the  soundness  of  our  judgment  before  accept- 
ing our  Hercules.  This  requires  a  master.  Clerk- 
Maxwell,  who  never  left  his  native  island  to  visit  our 
shores,  is  entitled  to  honor  as  a  promoter  of  American 
science  for  seeing  the  lion's  paw  in  the  early  efforts 
of  Rowland,  for  which  the  latter  was  unable  to  find 
a  medium  of  publication  in  his  own  country.  It 
must  also  be  admitted  that  the  task  is  more  serious 
now  than  it  was  then,  because,  from  the  constantly 
increasing  specialization  of  science,  it  has  become 
difficult  for  a  specialist  in  one  line  to  ascertain  the 
soundness  of  work  in  another. 

With  all  the  risks  that  may  be  involved  in  the 
proceeding,  it  will  be  quite  possible  to  select  an 
effective  body  of  leaders,  young  and  old,  with  whom 
an  institution  can  begin.  The  wants  of  these  men 
will  be  of  the  most  varied  kind.  One  needs  scarcely 
more  than  a  study  and  library;  another  must  have 
small  pieces  of  apparatus  which  he  can  perhaps  de- 
sign and  make  for  himself.  Another  may  need  ap-j 
paratus  and  appliances  so  expensive  that  only  an  in-j 
stitution  at  least  as  wealthy  as  an  ordinary  university 
would  be  able  to  supply  them.  The  apparatus  re- 
quired by  others  will  be  very  largely  human — assist- 
ants of  every  grade,  from  university  graduates  of  the 
highest  standing  down  to  routine  drudges  and  day- 
laborers.  Workrooms  there  must  be ;  but  it  is  hardly 
probable  that  buildings  and  laboratories  of  a  highly 
specialized  character  will  be  required  at  the  outset. 
The  best  counsel  will  be  necessary  at  every  step,  and 
in  this  respect  the  institution  must  start  from  simple 
beginnings  and  grow  slowly.  Leaders  must  be  added 

1 80 


ORGANIZATION  OF  SCIENTIFIC  RESEARCH 

one  by  one,  each  being  judged  by  those  who  have 
preceded  him  before  becoming  in  his  turn  a  member 
of  the  body.  As  the  body  grows  its  members  must 
be  kept  in  personal  touch,  talk  together,  pull  to- 
gether, and  act  together. 

The  writer  submits  these  views  to  the  great  body 
of  his  fellow-citizens  interested  in  the  promotion  of 
American  science  with  the  feeling  that,  though  his 
conclusions  may  need  amendment  in  details,  they 
rest  upon  facts  of  the  past  and  present  which  have 
not  received  the  consideration  which  they  merit. 
What  he  most  strongly  urges  is  that  the  whole  sub- 
ject of  the  most  efficient  method  of  promoting  re- 
search upon  a  higher  plane  shall  be  considered  with 
special  reference  to  conditions  in  our  own  country; 
and  that  the  lessons  taught  by  the  history  and  prog- 
ress of  scientific  research  in  all  countries  shall  be  fully 
weighed  and  discussed  by  those  most  interested  in 
making  this  form  of  effort  a  more  important  feature 
of  our  national  life.  When  this  is  done,  he  will  feel 
that  his  purpose  in  inviting  special  consideration  to 
his  individual  views  has  been  in  great  measure 
reached. 


XII 

CAN   WE   MAKE   IT   RAIN? 

nPO  the  uncritical  observer  the  possible  achieve- 
1  merits  of  invention  and  discovery  seem  bound- 
less. Half  a  century  ago  no  idea  could  have  appeared 
more  visionary  than  that  of  holding  communication 
in  a  few  seconds  of  time  with  our  fellows  in  Australia, 
or  having  a  talk  going  on  viva  voce  between  a  man  in 
Washington  and  another  in  Boston.  The  actual  at- 
tainment of  these  results  has  naturally  given  rise  to 
the  belief  that  the  word  "  impossible  "  has  disappeared 
from  our  vocabulary.  To  every  demonstration  that 
a  result  cannot  be  reached  the  answer  is,  Did  not  one 
Lardner,  some  sixty  years  ago,  demonstrate  that  a 
steamship  could  not  cross  the  Atlantic?  If  we  say 
that  for  every  actual  discovery  there  are  a  thousand 
visionary  projects,  we  are  told  that,  after  all,  any 
given  project  may  be  the  one  out  of  the  thousand. 

In  a  certain  way  these  hopeful  anticipations  are 
justified.  We  cannot  set  any  limit  either  to  the  dis- 
covery of  new  laws  of  nature  or  to  the  ingenious 
combination  of  devices  to  attain  results  which  now 
look  impossible.  The  science  of  to-day  suggests  a 
boundless  field  of  possibilities.  It  demonstrates  that 
the  heat  which  the  sun  radiates  upon  the  earth  in  a 
single  day  would  suffice  to  drive  all  the  steamships 
now  on  the  ocean  and  run  all  the  machinery  on  the 

182 


CAN    WE    MAKE    IT    RAIN? 

land  for  a  thousand  years.  The  only  difficulty  is  how 
to  concentrate  and  utilize  this  wasted  energy.  From 
the  stand-point  of  exact  science  aerial  navigation  is 
a  very  simple  matter.  We  have  only  to  find  the 
proper  combination  of  such  elements  as  weight,  pow- 
er, and  mechanical  force.  Whenever  Mr.  Maxim 
can  make  an  engine  strong  and  light  enough,  and 
sails  large,  strong,  and  light  enough,  and  devise  the 
machinery  required  to  connect  the  sails  and  engine, 
he  will  fly.  Science  has  nothing  but  encouraging 
words  for  his  project,  so  far  as  general  principles  are 
concerned.  Such  being  the  case,  I  am  not  going  to 
maintain  that  we  can  never  make  it  rain. 

But  I  do  maintain  two  propositions.  If  we  are 
ever  going  to  make  it  rain,  or  produce  any  other  re- 
sult hitherto  unattainable,  we  must  employ  adequate 
means.  And  if  any  proposed  means  or  agency  is 
already  familiar  to  science,  we  may  be  able  to  de- 
cide beforehand  whether  it  is  adequate.  Let  us 
grant  that  out  of  a  thousand  seemingly  visionary 
projects  one  is  really  sound.  Must  we  try  the  entire 
thousand  to  find  the  one?  By  no  means.  The 
chances  are  that  nine  hundred  of  them  will  involve 
no  agency  that  is  not  already  fully  understood,  and 
may,  therefore,  be  set  aside  without  even  being  tried. 
To  this  class  belongs  the  project  of  producing  rain 
by  sound.  As  I  write,  the  daily  journals  are  an- 
nouncing the  brilliant  success  of  experiments  in  this 
direction;  yet  I  unhesitatingly  maintain  that  sound 
cannot  make  rain,  and  propose  to  adduce  all  neces- 
sary proof  of  my  thesis.  The  nature  of  sound  is 
fully  understood,  and  so  are  the  conditions  under 
which  the  aqueous  vapor  in  the  atmosphere  may  be 
condensed.  Let  us  see  how  the  case  stands. 
13  183 


SIDE-LIGHTS     ON    ASTRONOMY 

A  room  of  average  size,  at  ordinary  temperature 
and  under  usual  conditions,  contains  about  a  quart 
of  water  in  the  form  of  invisible  vapor.  The  whole 
atmosphere  is  impregnated  with  vapor  in  about  the 
same  proportion.  We  must,  however,  distinguish  be- 
tween this  invisible  vapor  and  the  clouds  or  other 
visible  masses  to  which  the  same  term  is  often  ap-; 
plied.  The  distinction  may  be  very  clearly  seen  by 
watching  the  steam  coming  from  the  spout  of  a  boil- 
ing kettle.  Immediately  at  the  spout  the  escaping 
steam  is  transparent  and  invisible;  an  inch  or  two. 
away  a  white  cloud  is  formed,  which  we  commonly 
call  steam,  and  which  is  seen  belching  out  to  a  dis- 
tance of  one  or  more  feet,  and  perhaps  filling  a  con- 
siderable space  around  the  kettle;  at  a  still  greater 
distance  this  cloud  gradually  disappears.  Properly 
speaking,  the  visible  cloud  is  not  vapor  or  steam  at 
all,  but  minute  particles  or  drops  of  water  in  a  liquid 
state.  The  transparent  vapor  at  the  mouth  of  the 
kettle  is  the  true  vapor  of  water,  which  is  condensed 
into  liquid  drops  by  cooling;  but  after  being  diffused 
through  the  air  these  drops  evaporate  and  again 
become  true  vapor.  Clouds,  then,  are  not  formed  of 
true  vapor,  but  consist  of  impalpable  particles  of 
liquid  water  floating  or  suspended  in  the  air. 

But  we  all  know  that  clouds  do  not  always  fall  as 
rain.  In  order  that  rain  may  fall  the  impalpable 
particles  of  water  which  form  the  cloud  must  collect 
into  sensible  drops  large  enough  to  fall  to  the  earth.  : 
Two  steps  are  therefore  necessary  to  the  formation 
of  rain:  the  transparent  aqueous  vapor  in  the  air 
must  be  condensed  into  clouds,  and  the  material  of 
the  clouds  must  agglomerate  into  raindrops. 

No  physical  fact  is  better  established  than  that, 

184 


CAN    WE    MAKE    IT    RAIN? 

under  the  conditions  which  prevail  in  the  atmos- 
phere, the  aqueous  vapor  of  the  air  cannot  be  con- 
densed into  clouds  except  by  cooling.  It  is  true 
that  in  our  laboratories  it  can  be  condensed  by  com- 
pression. But,  for  reasons  which  I  need  not  explain, 
condensation  by  compression  cannot  take  place  in 
the  air.  The  cooling  which  results  in  the  formation 
of  clouds  and  rain  may  come  in  two  ways.  Rains 
which  last  for  several  hours  or  days  are  generally 
produced  by  the  intermixture  of  currents  of  air  of 
different  temperatures.  A  current  of  cold  air  meet- 
ing a  current  of  warm,  moist  air  in  its  course  may 
condense  a  considerable  portion  of  the  moisture  into 
clouds  and  rain,  and  this  condensation  will  go  on  as 
long  as  the  currents  continue  to  meet.  In  a  hot 
spring  day  a  mass  of  air  which  has  been  warmed  by 
the  sun,  and  moistened  by  evaporation  near  the  sur- 
face of  the  earth,  may  rise  up  and  cool  by  expansion 
to  near  the  freezing-point.  The  resulting  condensa- 
tion of  the  moisture  may  then  produce  a  shower  or 
thunder-squall.  But  the  formation  of  clouds  in  a 
clear  sky  without  motion  of  the  air  or  change  in 
the  temperature  of  the  vapor  is  simply  impossible. 
We  know  by  abundant  experiments  that  a  mass  of 
true  aqueous  vapor  will  never  condense  into  clouds 
or  drops  so  long  as  its  temperature  and  the  pressure 
of  the  air  upon  it  remain  unchanged. 

Now  let  us  consider  sound  as  an  agent  for  chang- 
ing the  state  of  things  in  the  air.  It  is  one  of  the 
commonest  and  simplest  agencies  in  the  world,  which 
we  can  experiment  upon  without  difficulty.  It  is 
purely  mechanical  in  its  action.  When  a  bomb  ex- 
plodes, a  certain  quantity  of  gas,  say  five  or  six  cubic 
yards,  is  suddenly  produced.  It  pushes  aside  and 

1*5 


SIDE-LIGHTS    ON    ASTRONOMY 

compresses  the  surrounding  air  in  all  directions,  and 
this  motion  and  compression  are  transmitted  from 
one  portion  of  the  air  to  another.  The  amount  of 
motion  diminishes  as  the  square  of  the  distance;  a? 
simple  calculation  shows  that  at  a  quarter  of  a  mile 
from  the  point  of  explosion  it  would  not  be  one  ten- 
thousandth  of  an  inch.  The  condensation  is  only 
momentary ;  it  may  last  the  hundredth  or  the  thou- 
sandth of  a  second,  according  to  the  suddenness  and 
violence  of  the  explosion;  then  elasticity  restores  the 
air  to  its  original  condition  and  everything  is  just  as 
it  was  before  the  explosion.  A  thousand  detonations 
can  produce  no  more  effect  upon  the  air,  or  upon 
the  watery  vapor  in  it,  than  a  thousand  rebounds  of 
a  small  boy's  rubber  ball  would  produce  upon  a  stone- 
wall. So  far  as  the  compression  of  the  air  could 
produce  even  a  momentary  effect,  it  would  be  to 
prevent  rather  than  to  cause  condensation  of  its 
vapor,  because  it  is  productive  of  heat,  which  pro- 
duces evaporation,  not  condensation. 

The  popular  notion  that  sound  may  produce  rain 
is  founded  principally  upon  the  supposed  fact  that 
great  battles  have  been  followed  by  heavy  rains. 
This  notion,  I  believe,  is  not  confirmed  by  statistics; 
but,  whether  it  is  or  not,  we  can  say  with  confidence 
that  it  was  not  the  sound  of  the  cannon  that  pro- 
duced the  rain.  That  sound  as  a  physical  factor  is 
quite  insignificant  would  be  evident  were  it  not  for 
our  fallacious  way  of  measuring  it.  The  human  ear 
is  an  instrument  of  wonderful  delicacy,  and  when  its 
tympanum  is  agitated  by  a  sound  we  call  it  a  "  con- 
cussion," when,  in  fact,  all  that  takes  place  is  a  sud- 
den motion  back  and  forth  of  a  tenth,  a  hundredth, 
or  a  thousandth  of  an  inch,  accompanied  by  a  slight 

186 


CAN    WE    MAKE    IT    RAIN? 

momentary  condensation.  After  these  motions  are 
completed  the  air  is  exactly  in  the  same  condition  as 
it  was  before ;  it  is  neither  hotter  nor  colder ;  no  cur- 
rent has  been  produced,  no  moisture  added. 

If  the  reader  is  not  satisfied  with  this  explanation, 
he  can  try  a  very  simple  experiment  which  ought  to 
be  conclusive.  If  he  will  explode  a  grain  of  dyna- 
mite, the  concussion  within  a  foot  of  the  point  of 
explosion  will  be  greater  than  that  which  can  be 
produced  by  the  most  powerful  bomb  at  a  distance 
of  a  quarter  of  a  mile.  In  fact,  if  the  latter  can  con- 
dense vapor  a  quarter  of  a  mile  away,  then  anybody 
can  condense  vapor  in  a  room  by  slapping  his  hands. 
Let  us,  therefore,  go  to  work  slapping  our  hands, 
and  see  how  long  we  must  continue  before  a  cloud 
begins  to  form. 

What  we  have  just  said  applies  principally  to  the 
condensation  of  invisible  vapor.  It  may  be  asked 
whether,  if  clouds  are  already  formed,  something 
may  not  be  done  to  accelerate  their  condensation 
into  raindrops  large  enough  to  fall  to  the  ground. 
This  also  may  be  the  subject  of  experiment.  Let 
us  stand  in  the  steam  escaping  from  a  kettle  and 
slap  our  hands.  We  shall  see  whether  the  steam 
condenses  into  drops.  I  am  sure  the  experiment 
will  be  a  failure;  and  no  other  conclusion  is  possible 
than  that  the  production  of  rain  by  sound  or  ex- 
i  plosions  is  out  of  the  question. 

It  must,  however,  be  added  that  the  laws  under 
:  which  the  impalpable  particles  of  water  in  clouds 
•  agglomerate  into  drops  of  rain  are  not  yet  under- 
stood, and  that  opinions  differ  on  this  subject.  Ex- 
|  periments  to  decide  the  question  are  needed,  and  it 
I  is  to  be  hoped  that  the  Weather  Bureau  will  under- 

187 


SIDE-LIGHTS    ON    ASTRONOMY 

take  them.  For  anything  we  know  to  the  contrary, 
the  agglomeration  may  be  facilitated  by  smoke  in 
the  air.  If  it  be  really  true  that  rains  have  been 
produced  by  great  battles,  we  may  say  with  con- 
fidence that  they  were  produced  by  the  smoke  from 
the  burning  powder  rising  into  the  clouds  and  form- 
ing nuclei  for  the  agglomeration  into  drops,  and  not 
by  the  mere  explosion.  If  this  be  the  case,  if  it  was 
the  smoke  and  not  the  sound  that  brought  the  rain, 
then  by  burning  gunpowder  and  dynamite  we  are 
acting  much  like  Charles  Lamb's  Chinamen  who 
practised  the  burning  of  their  houses  for  several 
centuries  before  finding  out  that  there  was  any 
cheaper  way  of  securing  the  coveted  delicacy  of 
roast  pig. 

But  how,  it  may  be  asked,  shall  we  deal  with  the 
fact  that  Mr.  Dyrenforth's  recent  explosions  of 
bombs  under  a  clear  sky  in  Texas  were  followed  in' 
a  few  hours,  or  a  day  or  two,  by  rains  in  a  region 
where  rain  was  almost  unknown?  I  know  too  little 
about  the  fact,  if  such  it  be,  to  do  more  than  ask 
questions  about  it  suggested  by  well-known  scientific 
truths.  If  there  is  any  scientific  result  which  we  can ! 
accept  with  confidence,  it  is  that  ten  seconds  after 
the  sound  of  the  last  bomb  died  away,  silence  resumed 
her  sway.  From  that  moment  everything  in  the 
air — humidity,  temperature,  pressure,  and  motion- 
was  exactly  the  same  as  if  no  bomb  had  been  fired.  J 
Now,  what  went  on  during  the  hours  that  elapsed 
between  the  sound  of  the  last  bomb  and  the  falling 
of  the  first  drop  of  rain?  Did  the  aqueous  vapor 
already  in  the  surrounding  air  slowly  condense  into 
clouds  and  raindrops  in  defiance  of  physical  laws? 
If  not,  the  hours  must  have  been  occupied  by  the 

188 


CAN    WE    MAKE    IT    RAIN? 

passage  of  a  mass  of  thousands  of  cubic  miles  of 
warm,  moist  air  coming  from  some  other  region  to 
which  the  sound  could  not  have  extended.  Or  was 
Jupiter  Pluvius  awakened  by  the  sound  after  two 
thousand  years  of  slumber,  and  did  the  laws  of 
nature  become  silent  at  his  command?  When  we 
transcend  what  is  scientifically  possible,  all  supposi- 
tions are  admissible ;  and  we  leave  the  reader  to  take 
his  choice  between  these  and  any  others  he  may 
choose  to  invent. 

One  word  in  justification  of  the  confidence  with 
which  I  have  cited  established  physical  laws.  It  is 
very  generally  supposed  that  most  great  advances 
in  applied  science  are  made  by  rejecting  or  disprov- 
ing the  results  reached  by  one's  predecessors.  Noth- 
ing could  be  farther  from  the  truth.  As  Huxley  has 
truly  said,  the  army  of  science  has  never  retreated 
from  a  position  once  gained.  Men  like  Ohm  and 
Maxwell  have  reduced  electricity  to  a  mathematical 
science,  and  it  is  by  accepting,  mastering,  and  ap- 
plying the  laws  of  electric  currents  which  they  dis- 
covered and  expounded  that  the  electric  light,  elec- 
tric railway,  and  all  other  applications  of  electricity 
have  been  developed.  It  is  by  applying  and  utiliz- 
ing the  laws  of  heat,  force,  and  vapor  laid  down  by 
such  men  as  Carnot  and  Regnault  that  we  now  cross 
the  Atlantic  in  six  days.  These  same  laws  govern 
the  condensation  of  vapor  in  the  atmosphere;  and  I 
say  with  confidence  that  if  we  ever  do  learn  to  make 
it  rain,  it  will  be  by  accepting  and  applying  them, 
and  not  by  ignoring  or  trying  to  repeal  them. 

How  much  the  indisposition  of  our  government  to 
secure  expert  scientific  evidence  may  cost  it  is  strik- 
ingly shown  by  a  recent  example.  It  expended 

189 


SIDE-LIGHTS    ON    ASTRONOMY 

several  million  dollars  on  a  tunnel  and  water-works 
for  the  city  of  Washington,  and  then  abandoned  the 
whole  work.  Had  the  project  been  submitted  to  a 
commission  of  geologists,  the  fact  that  the  rock-bed 
under  the  District  of  Columbia  would  not  stand  the 
continued  action  of  water  would  have  been  immediate- 
ly reported,  and  all  the  money  expended  would  have 
been  saved.  The  fact  is  that  there  is  very  little  to  ex- 
cite popular  interest  in  the  advance  of  exact  science. 
Investigators  are  generally  quiet,  unimpressive  men, 
rather  diffident,  and  wholly  wanting  in  the  art  of  in- 
teresting the  public  in  their  work.  It  is  safe  to  say 
that  neither  Lavoisier,  Galvani,  Ohm,  Regnault,  nor 
Maxwell  could  have  gotten  the  smallest  appropria- 
tion through  Congress  to  help  make  discoveries  which 
are  now  the  pride  of  our  century.  They  all  dealt  in 
facts  and  conclusions  quite  devoid  of  that  grandeur 
which  renders  so  captivating  the  project  of  attack- 
ing the  rains  in  their  aerial  stronghold  with  dynamite 
bombs. 


XIII 

THE    ASTRONOMICAL    EPHEMERIS    AND    THE 
NAUTICAL    ALMANAC* 


A  LTHOUGH  the  Nautical  Almanacs  of  the  world, 
r\  at  the  present  time,  are  of  comparatively  recent 
origin,  they  have  grown  from  small  beginnings,  the 
tracing  of  which  is  not  unlike  that  of  the  origin  of 
species  by  the  naturalist  of  the  present  day.  Not- 
withstanding its  familiar  name,  it  has  always  been 
designed  rather  for  astronomical  than  for  nautical 
purposes.  Such  a  publication  would  have  been  of  no 
use  to  the  navigator  before  he  had  instruments  with 
which  to  measure  the  altitudes  of  the  heavenly  bodies. 
The  earlier  navigators  seldom  ventured  out  of  sight  of 
land,  and  during  the  night  they  are  said  to  have  steer- 
ed by  the  "Cynosure"  or  constellation  of  the  Great 
Bear,  a  practice  which  has  brought  the  name  of  the 
constellation  into  our  language  of  the  present  day  to 
designate  an  object  on  which  all  eyes  are  intently  fix- 
ed. This  constellation  was  a  little  nearer  the  pole  in 
former  ages  than  at  the  present  time ;  still  its  distance 
was  always  so  great  that  its  use  as  a  mark  of  the 
northern  point  of  the  horizon  does  not  inspire  us  with 
great  respect  for  the  accuracy  with  which  the  ancient 
navigators  sought  to  shape  their  course. 

The  Nautical  Almanac  of  the  present  day  had  its 

*  Read  before  the  U.  S.  Naval  Institute,  January  10,  1879. 
191 


SIDE-LIGHTS    ON    ASTRONOMY 

origin  in  the  Astronomical  Ephemerides  called  forth 
•by  the  needs  of  predictions  of  celestial  motions  both 
on  the  part  of  the  astronomer  and  the  citizen.  So 
long  as  astrology  had  a  firm  hold  on  the  minds  of  men, 
the  positions  of  the  planets  were  looked  to  with  great 
interest.  The  theories  of  Ptolemy,  although  founded 
on  a  radically  false  system,  nevertheless  sufficed  to 
predict  the  position  of  the  sun,  moon,  and  planets, 
with  all  the  accuracy  necessary  for  the  purposes  of 
the  daily  life  of  the  ancients  or  the  sentences  of  their 
astrologers.  Indeed,  if  his  tables  were  carried  down 
to  the  present  time,  the  positions  of  the  heavenly 
bodies  would  be  so  few  degrees  in  error  that  their 
recognition  would  be  very  easy.  The  times  of  most 
of  the  eclipses  would  be  predicted  within  a  few  hours, 
and  the  conjunct  ons  of  the  planets  within  a  few 
days.  Thus  it  was  possible  for  the  astronomers  of 
the  Middle  Ages  to  prepare  for  their  own  use,  and 
that  of  the  people,  certain  rude  predictions  respect- 
ing the  courses  of  the  sun  and  moon  and  the  aspect 
of  the  heavens,  which  served  the  purpose  of  daily 
life  and  perhaps  lessened  the  confusion  arising  from 
their  complicated  calendars.  In  the  signs  of  the 
zodiac  and  the  different  effects  which  follow  from 
the  sun  and  moon  passing  from  sign  to  sign,  still 
found  in  our  farmers'  almanacs,  we  have  the  dying 
traces  of  these  ancient  ephemerides. 

The  great  Kepler  was  obliged  to  print  an  astro- 
logical almanac  in  virtue  of  his  position  as  astrono-  • 
mer  of  the  court  of  the  King  of  Austria.  But,  not- 
withstanding the  popular  belief  that  astronomy  had 
its  origin  in  astrology,  the  astronomical  writings  of 
all  ages  seem  to  show  that  the  astronomers  proper 
never  had  any  belief  in  astrology.  To  Kepler  him- 

192 


THE    ASTRONOMICAL    ETHEMERIS 

self  the  necessity  for  preparing  this  almanac  was  a 
humiliation  to  which  he  submitted  only  through  the 
pressure  of  poverty.  Subsequent  ephemerides  were 
prepared  with  more  practical  objects.  They  gave 
the  longitudes  of  the  planets,  the  position  of  the  sun, 
the  time  of  rising  and  setting,  the  prediction  of 
eclipses,  etc. 

They  have,  of  course,  gradually  increased  in  ac- 
curacy as  the  tables  of  the  celestial  motions  were 
improved  from  time  to  time.  At  first  they  were  not 
regular,  annual  publications,  issued  by  governments, 
as  at  the  present  time,  but  the  works  of  individual 
astronomers  who  issued  their  ephemerides  for  several 
years  in  advance,  at  irregular  intervals.  One  man 
might  issue  one,  two,  or  half  a  dozen  such  volumes, 
as  a  private  work,  for  the  benefit  of  his  fellows,  and 
each  might  cover  as  many  years  as  he  thought  proper. 

The  first  publication  of  this  sort,  which  I  have  in 
my  possession,  is  the  Ephemerides  of  Manfredi,  of 
Bonn,  computed  for  the  years  1715  to  1725,  in  two 
volumes. 

Of  the  regular  annual  ephemerides  the  earliest, 
so  far  as  I  am  aware,  is  the  Connaissance  des  Temps 
or  French  Nautical  Almanac.  The  first  issue  was 
in  the  year  1679,  by  Picard,  and  it  has  been  con- 
tinued without  interruption  to  the  present  time. 
Its  early  numbers  were,  of  course,  very  small,  and 
meagre  in  their  details.  They  were  issued  by  the  as- 
tronomers of  the  French  Academy  of  Sciences,  under 
the  combined  auspices  of  the  academy  and  the  gov- 
ernment. They  included  not  merely  predictions  from 
the  tables,  but  also  astronomical  observations  made 
at  the  Paris  Observatory  or  elsewhere.  When  the 
Bureau  of  Longitudes  was  created  in  1795,  the  prep- 


SIDE-LIGHTS    ON    ASTRONOMY 

aration  of  the  work  was  intrusted   to   it,  and  has  | 
remained  in  its  charge  until  the  present  time.     As 
it  is  the  oldest,  so,  in  respect  at  least  to  number  of 
pages,  it  is  the  largest  ephemeris  of  the  present  time.  ; 
The  astronomical  portion  of  the  volume  for  1879  fills 
more  than  seven  hundred  pages,  while  the  table  of 
geographical    positions,    which    has    always    been   a 
feature  of  the  work,   contains  nearly  one  hundred 
pages  more. 

The  first  issue  of  the  British  Nautical  Almanac  was 
that  for  the  year  1767  and  appeared  in  1766.  It  dif- 
fers from  the  French  Almanac  in  owing  its  origin 
entirely  to  the  needs  of  navigation.  The  British 
nation,  as  the  leading  maritime  power  of  the  world, 
was  naturally  interested  in  the  discovery  of  a  method 
by  which  the  longitude  could  be  found  at  sea.  As 
most  of  my  hearers  are  probably  aware,  there  was,  j 
for  many  years,  a  standing  offer  by  the  British  gov- 
ernment, of  ten  thousand  pounds  for  the  discovery 
of  a  practical  and  sufficiently  accurate  method  of 
attaining  this  object.  If  I  am  rightly  informed,  the 
requirement  was  that  a  ship  should  be  able  to  deter- 
mine the  Greenwich  time  within  two  minutes,  after 
being  six  months  at  sea.  When  the  office  of  Astron- 
omer Royal  was  established  in  1765,  the  duty  of  the  ; 
incumbent  was  declared  to  be  "to  apply  himself 
with  the  most  exact  care  and  diligence  to  the  rectify- 
ing the  Tables  of  the  Motions  of  the  Heavens,  and 
the  places  of  the  Fixed  Stars  in  order  to  find  out  the 
so  much  desired  Longitude  at  Sea  for  the  perfecting 
the  Art  of  Navigation." 

About  the  middle  of  the  last  century  the  lunar 
tables  were  so  far  improved  that  Dr.  Maskelyne  con- 
sidered them  available  for  attaining  this  long-wished- 

194 


THE    ASTRONOMICAL    EPHEMERIS 

for  object.  The  method  which  I  think  was  then,  for 
the  first  time,  proposed  was  the  now  familiar  one  of 
lunar  distances.  Several  trials  of  the  method  were 
made  by  accomplished  gentlemen  who  considered 
that  nothing  was  wanting  to  make  it  practical  at 
sea  but  a  Nautical  Ephemeris.  The  tables  of  the 
moon,  necessary  for  the  purpose,  were  prepared  by 
Tobias  Mayer,  of  Gottingen,  and  the  regular  annual 
issue  of  the  work  was  commenced  in  1766,  as  already 
stated.  Of  the  reward  which  had  been  offered,  three 
thousand  pounds  were  paid  to  the  widow  of  Mayer, 
and  three  thousand  pounds  to  the  celebrated  mathe- 
matician Euler  for  having  invented  the  methods  used 
by  Mayer  in  the  construction  of  his  tables.  The  is- 
sue of  the  Nautical  Ephemeris  was  intrusted  to  Dr. 
Maskelyne.  Like  other  publications  of  this  sort  this 
ephemeris  has  gradually  increased  in  volume.  Dur- 
ing the  first  sixty  or  seventy  years  the  data  were  ex- 
tremely meagre,  including  only  such  as  were  con- 
sidered necessary  for  the  determination  of  positions. 

In  1830  the  subject  of  improving  the  Nautical 
Almanac  was  referred  by  the  Lord  Commissioners 
of  the  Admiralty  to  a  committee  of  the  Astronomi- 
cal Society  of  London.  A  subcommittee,  including 
eleven  of  the  most  distinguished  astronomers  and 
one  scientific  navigator,  made  an  exhaustive  report, 
recommendihg  a  radical  rearrangement  and  im- 
provement of  the  work.  The  recommendations  of 
this  committee  were  first  carried  into  effect  in  the 
Nautical  Almanac  for  the  year  1834.  The  arrange- 
ment of  the  Navigator's  Ephemeris  then  devised  has 
been  continued  in  the  British  Almanac  to  the  present 
time. 

A  good  deal  of  matter  has  been  added  to  the  Brit- 


SIDE-LIGHTS    ON    ASTRONOMY 

ish  Almanac  during  the  forty  years  and  upwards 
which  have  elapsed,  but  it  has  been  worked  in  rather 
by  using  smaller  type  and  closer  printing  than  by 
increasing  the  number  of  pages.  The  almanac  for 
1834  contains  five  hundred  and  seventeen  pages  and 
that  for  1880  five  hundred  and  nineteen  pages.  The 
general  aspect  of  the  page  is  now  somewhat  crowded, 
yet,  considering  the  quantity  of  figures  on  each  page 
the  arrangement  is  marvellously  clear  and  legible. 

The  Spanish  Almanaque  Nautico  has  been  issued 
since  the  beginning  of  the  century.  Like  its  fellows 
it  has  been  gradually  enlarged  and  improved,  in  recent 
times,  and  is  now  of  about  the  same  number  of  pages 
with  the  British  and  American  almanacs.  As  a  rule 
there  is  less  matter  on  a  page,  so  that  the  data  act- 
ually given  are  not  so  complete  as  in  some  other 
publications. 

In  Germany  two  distinct  publications  of  this  class 
are  issued,  the  one  purely  astronomical,  the  other 
purely  nautical. 

The  astronomical  publication  has  been  issued  for 
more  than  a  century  under  the  title  of  Berliner 
Astronomisches  Jahrbuch.  It  is  intended  principal- 
ly for  the  theoretical  astronomer,  and  in  respect  to 
matter  necessary  to  the  determinations  of  positions 
on  the  earth  it  is  rather  meagre.  It  is  issued  by  the 
Berlin  Observatory,  at  the  expense  of  the  govern- 
ment. 

The  companion  of  this  work,  intended  for  the  use 
of  the  German  marine,  is  the  Nautisches  Jahrbuch, 
prepared  and  issued  under  the  direction  of  the  min- 
ister of  commerce  and  public  works.  It  is  copied 
largely  from  the  British  Nautical  Almanac,  and  in 
respect  to  arrangement  and  data  is  similar  to  our 

196 


THE    ASTRONOMICAL    EPHEMERIS 

American  Nautical  Almanac,  prepared  for  the  use 

!  of  navigators,  giving,  however,  more  matter,  but  in 

a  less  convenient  form.     The  right  ascension  and 

declination  of  the  moon  are  given  for  every  three 

hours  instead  of  for  every  hour;  one  page  of  each 

|  month  is  devoted  to  eclipses  of  Jupiter's  satellites, 

1  phenomena  which  we   never  consider  necessary  in 

the  nautical  portion  of  our  own  almanac.     At  the 

end  of  the  work  the  apparent  positions  of  seventy  or 

eighty  of  the  brightest  stars  are  given  for  every  ten 

days,  while  it  is  considered  that  our  own  navigators 

will  be  satisfied  with  the.  mean  places  for  the  begin- 

;  ning  of  the  year.     At  the  end  is  a  collection  of  tables 

which  I  doubt  whether  any  other  than  a  German 

navigator  would  ever  use.     Whether  they  use  them 

jor  not  I  am  not  prepared  to  say. 

The  preceding  are  the  principal  astronomical  and 
i  nautical  ephemerides  of  the  world,  but  there  are  a 
.number  of  minor  publications,  of  the  same  class,  of 
which    I   cannot   pretend   to   give   a   complete   list. 
Among  them  is  the  Portuguese  Astronomical  Ephem- 
:eris  for  the  meridian  of  the  University  of  Coimbra, 
prepared  for  Portuguese  navigators.     I  do  not  know 
(Whether    the    Portuguese    navigators    really    reckon 
i  their  longitudes  from  this  point :  if  they  do  the  prac- 
,tice  must  be  attended  with  more  or  less  confusion. 
'All  the  matter  is  given  by  months,  as  in  the  solar 
<and  lunar  ephemeris    of    our   own  and  the  British 
'Almanac.     For  the  sun  we  have  its  longitude,  right 
ascension,  and  declination,  all  expressed  in  arc  and 
not  in  time.     The  equation  of  time  and  the  side- 
real  time   of   mean   noon   complete   the   ephemeris 
'proper.     The  positions  of  the  principal  planets  are 
'given  in  no  case  oftener  than  for  every  third  day. 

197 


SIDE-LIGHTS    ON    ASTRONOMY 

The  longitude  and  latitude  of  the  moon  are  given 
for  noon  and  midnight.  One  feature  not  found  in 
any  other  almanac  is  the  time  at  which  the  moon 
enters  each  of  the  signs  of  the  zodiac.  It  may  be 
supposed  that  this  information  is  designed  rather 
for  the  benefit  of  the  Portuguese  landsman  than  of 
the  navigator.  The  right  ascensions  and  declinations 
of  the  moon  and  the  lunar  distances  are  also  given 
for  intervals  of  twelve  hours.  Only  the  last  page 
gives  the  eclipses  of  the  satellites  of  Jupiter.  The 
Fixed  Stars  are  wholly  omitted. 

An  old  ephemeris,  and  one  well  known  in  astronomy 
is  that  published  by  the  Observatory  of  Milan,  Italy, 
which  has  lately  entered  upon  the  second  century  of 
its  existence.  Its  data  are  extremely  meagre  and  of 
no  interest  whatever  to  the  navigator.  The  greater 
part  of  the  volume  is  taken  up  with  observations  at 
the  Milan  Observatory. 

Since  taking  charge  of  the  American  Ephemeris 
I  have  endeavored  to  ascertain  what  nautical  alma- 
nacs are  actually  used  by  the  principal  maritime  na- 
tions of  Europe.  I  have  been  able  to  obtain  none 
except  those  above  mentioned.  As  a  general  rule  I 
think  the  British  Nautical  Almanac  is  used  by  all 
the  northern  nations,  as  already  indicated.  The 
German  Nautical  Jahrbuch  is  principally  a  reprint 
from  the  British.  The  Swedish  navigators,  being  all 
well  acquainted  with  the  English  language,  use  the 
British  Almanac  without  change.  The  Russian  gov- 
ernment, however,  prints  an  explanation  of  the  various 
terms  in  the  language  of  their  own  people  and  binds 
it  in  at  the  end  of  the  British  Almanac.  This  ex- 
planation includes  translations  of  the  principal  terms 
used  in  the  heading  of  pages,  such  as  the  names  of 

198 


THE    ASTRONOMICAL    EPHEMERIS 

the  months  and  days,  the  different  planets,  con- 
stellations, and  fixed  stars,  and  the  phenomena  of 
angle  and  time.  They  have  even  an  index  of  their 
own  in  which  the  titles  of  the  different  articles  are 
given  in  Russian.  This  explanation  occupies,  in  all, 
seventy-five  pages  —  more  than  double  that  taken  up 
by  the  original  explanation. 

One  of  the  first  considerations  which  strikes  us  in 

comparing  these  multitudinous   publications    is   the 

confusion  which  must  arise  from  the  use  of  so  many 

meridians.     If  each  of  these  southern  nations,  the 

Spanish  and  Portuguese  for  instance,  actually  use«a 

meridian  of  their  own,   the  practice  must  lead  to 

!  great  confusion.     If  their  navigators  do  not  do  so 

i  but  refer  their  longitudes  to  the  meridian  of  Green- 

I  wich,  then  their  almanacs  must  be  as  good  as  use- 

j  less.     They  would  find  it  far  better  to  buy  an  ephem- 

j  eris  referred  to  the  meridian  of  Greenwich  than  to 

I  attempt  to  use  their  own.     The  northern  nations,  I 

think,  have  all  begun  to  refer  to  the  meridian  of 

;   Greenwich,  and  the  same  thing  is  happily  true  of  our 

I  own  marine.     We  may,  therefore,  hope  that  all  com- 

mercial nations  will,  before  long,  refer  their  longi- 

tudes to  one  and  the  same  meridian,  and  the  resulting 

;   confusion  be  thus  avoided. 

The  preparation  of  the  American  Ephemeris  and 
Nautical  Almanac  was  commenced  in   1849,  under 
the  superintendence  of  the  late  Rear-  Admiral,  then 
Lieutenant,  Charles  Henry  Davis.     The  first  volume 
!   to  be  issued  was  that  for  the  year  1855.     Both  in 
I  the  preparation  of  that  work  and  in  the  connected 
work  of  mapping  the  country,  the  question  of  the 
meridian  to  be  adopted  was  one  of  the  first  impor- 
'   tance,  and   received   great   attention   from^Admiral 


.4 


SIDE-LIGHTS    ON    ASTRONOMY 

Davis,  who  made  an  able  report  on  the  subject.  Our 
situation  was  in  some  respects  peculiar,  owing  to: 
the  great  distance  which  separated  us  from  Europe 
and  the  uncertainty  of  the  exact  difference  of  longi- 
tude between  the  two  continents.  It  was  hardly 
practicable  to  refer  longitudes  in  our  own  country 
to  any  European  meridian.  The  attempt  to  do  soi 
would  involve  continual  changes  as  the  transat-; 
lantic  longitude  was  from  time  to  time  corrected. 
On  the  other  hand,  in  order  to  avoid  confusion  in 
navigation,  it  was  essential  that  our  navigators 
should  continue  to  reckon  from  the  meridian  of 
Greenwich.  The  trouble  arising  from  uncertainty 
of  the  exact  longitude  does  not  affect  the  navigator, 
because,  for  his  purpose,  astronomical  precision  is 
not  necessary. 

The  wisest  solution  was  probably  that  embodied 
in  the  act  of  Congress,  approved  September  28,  1850, 
on  the  recommendation  of  Lieutenant  Davis,   if  I'l 
mistake  not.     "The  meridian  of  the  Observatory  at 
Washington  shall  be  adopted  and  used  as  the  Ameri- 
can meridian  for  all  astronomical  purposes,  and  the 
meridian    of    Greenwich    shall    be    adopted    for    all 
nautical  purposes."     The  execution  of  this  law  neces- 
sarily involves  the  question,    "What  shall  be  con- 
sidered astronomical  and  what  nautical  purposes  ?'| 
Whether  it  was  from  the  difficulty  of  deciding  this 
question,   or  from  nobody's  remembering  the  lawl 
the  latter  has  been  practically  a  dead  letter.     SurelyJ 
if  there  is  any  region  of  the  globe  which  the  law  in- 
tended should  be  referred  to  the  meridian  of  Wash- 
ington, it  is  the  interior  of  our  own  country.     Yet, 
notwithstanding  the  law,  all  acts  of  Congress  relating 
to  the  territories  have,  so  far  as  I  know,  referred 

200 


THE    ASTRONOMICAL    EPHEMERIS 

|  everything  to  the  meridian  of  Greenwich  and  not  to 
;  that  of  Washington.     Even  the  maps  issued  by  our 
I  various  surveys  are  referred  to   the  same   transat- 
lantic meridian.     The  absurdity  culminated  in  a  lo- 
i  cal  map  of  the  city  of  Washington  and  the  District 
of  Columbia,  issued  by  private  parties,  in  1861,  in 
i  which  we  find  even  the  meridians  passing  through 
I  the  city  of  Washington  referred  to  a  supposed  Green- 
j  wich. 

This  practice  has  led  to  a  confusion  which  may  not 
be  evident  at  first  sight,  but  which  is  so  great  and 
permanent   that  it  may  be  worth  explaining.     If, 
indeed,  we  could  actually  refer  all  our  longitudes  to 
j  an  accurate  meridian  of  Greenwich  in  the  first  place ; 
i  if,  for  instance,  any  western  region  could  be  at  once 
:  connected  by  telegraph  with  the  Greenwich  Observa- 
itory,  and  thus  exchange  longitude  signals  night  after 
i  night,  no  trouble  or  confusion  would  arise  from  re- 
!f erring   to   the   meridian   of   Greenwich.     But   this, 
practically,  cannot  be  done.     All  our  interior  longi- 
,tudes  have  been  and  are  determined  differentially  by 
comparison  with  some  point  in  this  country.     One 
;  j  of  the  most  frequent  points  of  reference  used  this 
jway  has  been  the  Cambridge  Observatory.     Suppose, 
| then,  a  surveyor  at  Omaha  makes  a  telegraphic  longi- 
Itude  determination  between  that  point  and  the  Cam- 
bridge Observatory.     Since  he  wants  his  longitude 
Ijreduced  to  Greenwich,  he  finds  some  supposed  longi- 
fjtude  of  the  Cambridge  Observatory  from  Greenwich 
•and  adds  that  to  his  own  longitude.     Thus,  what  he 
'gives  is  a  longitude  actually  determined,  plus  an  as- 
'  sumed  longitude  of  Cambridge,  and,  unless  the  as- 
jsumecl  longitude  of  Cambridge  is  distinctly  marked 
['on  his  maps,  we  may  not  know  what  it  is. 

201 


SIDE-LIGHTS    ON    ASTRONOMY 

After  a  while  a  second  party  determines  the  longiJ 
tude  of  Ogden  from  Cambridge.  In  the  mean  time, 
the  longitude  of  Cambridge  from  Greenwich  has  been 
corrected,  and  we  have  a  longitude  of  Ogden  which 
will  be  discordant  with  that  of  Omaha,  owing  to  the 
change  in  the  longitude  of  Cambridge.  A  third  party 
determines  the  longitudes  of,  let  us  suppose,  St. 
Louis  from  Washington,  he  adds  the  assumed  longi- 
tudes of  Washington  from  Greenwich  which  may  not 
agree  with  either  of  the  longitudes  of  Cambridge  and 
gets  his  longitude.  Thus  we  have  a  series  of  results 
for  our  western  longitude  all  nominally  referred  to 
the  meridian  of  Greenwich,  but  actually  referred  to 
a  confused  collection  of  meridians,  nobody  knows 
what.  If  the  law  had  only  provided  that  the  longi- 
tude of  Washington  from  Greenwich  should  be  in- 
variably fixed  at  a  certain  quantity,  say  77°  3',  this 
confusion  would  not  have  arisen.  It  is  true  that 
the  longitude  thus  established  by  law  might  not  have 
been  perfectly  correct,  but  this  would  not  cause  any 
trouble  nor  confusion.  Our  longitude  would  have 
been  simply  referred  to  a  certain  assumed  Greenwich, 
the  small  error  of  which  would  have  been  of  no  im- 
portance to  the  navigator  or  astronomer.  It  would 
have  differed  from  the  present  system  only  in  that 
the  assumed  Greenwich  would  have  been  invariable 
instead  of  dancing  about  from  time  to  time  as  it  has 
done  under  the  present  system.  You  understand 
that  when  the  astronomer,  in  computing  an  interior 
longitude,  supposes  that  of  Cambridge  from  Green- 
wich to  be  a  certain  definite  amount,  say  4h  44™  30*, 
what  he  actually  does  is  to  count  from  a  meridian 
just  that  far  east  of  Cambridge.  When  he  changes 
the  assumed  longitude  of  Cambridge  he  counts  from 

202 


THE    ASTRONOMICAL    EPHEMERIS 

a  meridian  farther  east  or  farther  west  of  his  former 
one:  in  other  words,  he  always  counts  from  an  as- 
sumed Greenwich,  which  changes  its  position  from 
.  time  to  time,  relative  to  our  own  country. 

Having  two  meridians  to  look  after,  the  form  of 

the  American  Ephemeris,  to  be  best  adapted  to  the 

•wants    both    of    navigators    and    astronomers    was 

necessarily  peculiar.     Had   our  navigators   referred 

1  their  longitudes  to  any  meridian  of  our  own  country 

!  the  arrangement  of  the  work  need  not  have  differed 

materially  from   that  of  foreign   ones.     But  being 

!  referred  to  a  meridian  far  outside  our  limits  and  at 

!  the  same  time  designed  for  use  within  those  limits, 

I  it  was  necessary  to  make  a  division  of  the  matter. 

!  Accordingly,  the   American   Ephemeris   has   always 

i  been  divided  into  two  parts :  the  first  for  the  use  of 

i  navigators,  referred  to  the  meridian  of  Greenwich, 

i  the  second  for  that  of  astronomers,  referred  to  the 

!  meridian  of  Washington.     The  division  of  the  matter 

without  serious  duplication  is  more  easy  than  might 

I  at  first  be  imagined.     In  explaining  it,  I  will  take  the 

ephemeris  as  it  now  is,  with  the  small  changes  which 

have  been  made  from  time  to  time. 

One  of  the  purposes  of  any  ephemeris,  and  espe- 
of  that  of  the  navigators,  is  to  give  the  position 
of  the  heavenly  bodies  at  equidistant  intervals  of 
1  time,  usually  one  day.  Since  it  is  noon  at  some  point 
'  of  the  earth  all  the  time,  it  follows  that  such  an 
*  ephemeris  will  always  be  referred  to  noon  at  some 
':  meridian.  What  meridian  this  shall  be  is  purely  a 
!  practical  question,  to  be  determined  by  convenience 
1  and  custom.  Greenwich  noon,  being  that  necessa- 
|  rily  used  by  the  navigator,  is  adopted  as  the  stand- 
1  ard,  but  we  must  not  conclude  that  the  ephemeris 

203 


I  daily 


SIDE-LIGHTS    ON    ASTRONOMY 

for  Greenwich  noon  is  referred  to  the  meridian  of 
Greenwich  in  the  sense  that  we  refer  a  longitude  to 
that  meridian.  Greenwich  noon  is  i8h  51™  48*, 
Washington  mean  time ;  so  the  ephemeris  which  gives 
data  for  every  Greenwich  noon  may  be  considered  as 
referred  to  the  meridian  of  Washington  giving  the 
data  for  iyh  51™  48s,  Washington  time,  every  day. 
The  rule  adopted,  therefore,  is  to  have  all  the  eph- 
emerides  which  refer  to  absolute  time,  without  any 
reference  to  a  meridian,  given  for  Greenwich  noon, 
unless  there  may  be  some  special  reason  to  the  con-i 
trary.  For  the  needs  of  the  navigator  and  the 
theoretical  astronomer  these  are  the  most  convenient 
epochs. 

Another  part  of  the  ephemeris  gives  the  position 
of  the  heavenly  bodies,  not  at  equidistant  intervals,.; 
but  at  transit  over  some  meridian.  For  this  purpose 
the  meridian  of  Washington  is  chosen  for  obvious 
reasons.  The  astronomical  part  of  our  ephemeris, 
therefore,  gives  the  positions  of  the  principal  fixed 
stars,  the  sun,  moon,  and  all  the  larger  planets  at  the 
moment  of  transit  over  our  own  meridian. 

The  third  class  of  data  in  the  ephemeris  comprises 
phenomena  to  be  predicted  and  observed.  Such  are 
eclipses  of  the  sun  and  moon,  occultations  of  fixed 
stars  by  the  moon,  and  eclipses  of  Jupiter's  satellites. 
These  phenomena  are  all  given  in  Washington  mean 
time  as  being  most  convenient  for  observers  in  our 
own  country.  There  is  a  partial  exception,  however, 
in  the  case  of  eclipses  of  the  sun  and  moon.  The 
former  are  rather  for  the  world  in  general  than  for 
our  own  country,  and  it  was  found  difficult  to  ar- 
range them  to  be  referred  to  the  meridian  of  Wash- 
ington without  having  the  maps  referred  to  the  same 

204 


THE    ASTRONOMICAL    EPHEMERIS 

meridian.  Since,  however,  the  meridian  of  Green- 
wich is  most  convenient  outside  of  our  own  territory, 
and  since  but  a  small  portion  of  the  eclipses  are  visi- 
ble within  it,  it  is  much  the  best  to  have  the  eclipses 
referred  entirely  to  the  meridian  of  Greenwich.  I 
am  the  more  ready  to  adopt  this  change  because 
when  the  eclipses  are  to  be  computed  for  our  own 
country  the  change  of  meridians  will  be  very  readily 
understood  by  those  who  make  the  computation. 

It  may  be  interesting  to  say  something  of  the 
tables  and  theories  from  which  the  astronomical  eph- 
emerides  are  computed.  To  understand  them  com- 
pletely it  is  necessary  to  trace  them  to  their  origin. 
The  problem  of  calculating  the  motions  of  the  heav- 
enly bodies  and  the  changes  in  the  aspect  of  the 
celestial  sphere  was  one  of  the  first  with  which  the 
students  of  astronomy  were  occupied.  Indeed,  in 
ancient  times,  the  only  astronomical  problems  which 
could  be  attacked  were  of  this  class,  for  the  simple 
reason  that  without  the  telescope  and  other  instru- 
ments of  research  it  was  impossible  to  form  any  idea 
of  the  physical  constitution  of  the  heavenly  bodies. 
To  the  ancients  the  stars  and  planets  were  simply 
points  or  surfaces  in  motion.  They  might  have 
guessed  that  they  were  globes  like  that  on  which  we 
live,  but  they  were  unable  to  form  any  theory  of  the 
nature  of  these  globes.  Thus,  in  The  Almagest  of 
Ptolemy,  the  most  complete  treatise  on  the  ancient 
astronomy  which  we  possess,  we  find  the  motions  of 
all  the  heavenly  bodies  carefully  investigated  and 
tables  given  for  the  convenient  computation  of  their 
positions.  Crude  and  imperfect  though  these  tables 
may  be,  they  were  the  beginnings  from  which  those 
now  in  use  have  arisen. 

205 


SIDE-LIGHTS    ON    ASTRONOMY 

No  radical  change  was  made  in  the  general  prin- 
ciples on  which  these  theories  and  tables  were  con- 
structed until  the  true  system  of  the  world  was 
propounded  by  Copernicus.  On  this  system  the 
apparent  motion  of  each  planet  in  the  epicycle  was 
represented  by  a  motion  of  the  earth  around  the  sun, 
and  the  problem  of  correcting  the  position  of  the 
planet  on  account  of  the  epicycle  was  reduced  to 
finding  its  geocentric  from  its  heliocentric  position. 
This  was  the  greatest  step  ever  taken  in  theoretical 
astronomy,  yet  it  was  but  a  single  step.  So  far  as 
the  materials  were  concerned  and  the  mode  of  repre- 
senting the  planetary  motions,  no  other  radical  ad- 
vance was  made  by  Copernicus.  Indeed,  it  is  re- 
markable that  he  introduced  an  epicycle  which  was 
not  considered  necessary  by  Ptolemy  in  order  to 
represent  the  inequalities  in  the  motions  of  the 
planets  around  the  sun. 

The  next  great  advance  made  in  the  theory  of  the 
planetary  motion  was  the  discovery  by  Kepler  of 
the  celebrated  laws  which  bear  his  name.  When  it 
was  established  that  each  planet  moved  in  an  ellipse 
having  the  sun  in  one  focus  it  became  possible  to 
form  tables  of  the  motions  of  the  heavenly  bodies 
much  more  accurate  than  had  before  been  known. 
Such  tables  were  published  by  Kepler  in  1632,  under 
the  name  of  Rudolphine  Tables,  in  memory  of  his 
patron,  the  Emperor  Rudolph.  But  the  laws  of 
Kepler  took  no  account  of  the  action  of  the  planets 
on  one  another.  It  is  well  known  that  if  each  planet 
moved  only  under  the  influence  of  the  gravitating 
force  of  the  sun  its  motion  would  accord  rigorously 
with  the  laws  of  Kepler,  and  the  problems  of  theo- 
retical astronomy  would  be  greatly  simplified.  When, 

206 


THE    ASTRONOMICAL    EPHEMERIS 

therefore,  the  results  of  Kepler's  laws  were  compared 
with  ancient  and  modern  observations  it  was  found 
that  they  were  not  exactly  represented  by  the  theory. 
It  was  evident  that  the  elliptic  orbits  of  the  planets 
were  subject  to  change,  but  it  was  entirely  beyond 
the  power  of  investigation,  at  that  time,  to  assign 
any  cause  for  such  changes.  Notwithstanding  the 
simplicity  of  the  causes  which  we  now  know  to  pro- 
duce them,  they  are  in  form  extremely  complex. 

.Without  the  knowledge  of  the  theory  of  gravitation 
it  would  be  entirely  out  of  the  question  to  form  any 
tables  of  the  panetary  motions  which  would  at  all 
satisfy  our  modern  astronomers. 

When  the  theory  of  universal  gravitation  was  pro- 
pounded by  Newton  he  showed  that  a  planet  sub- 
jected only  to  the  gravitation  of  a  central  body,  like 
the  sun,  would  move  in  exact  accordance  with  Kep- 
ler's laws.  But  by  his  theory  the  planets  must  attract 
one  another  and  these  attractions  must  cause  the 
motions  of  each  to  deviate  slightly  from  the  laws  in 
question.  Since  such  deviations  were  actually  ob- 
served it  was  very  natural  to  conclude  that  they 
were  due  to  this  cause,  but  how  shall  we  prove  it? 
To  do  this  with  all  the  rigor  required  in  a  mathe- 
matical investigation  it  is  necessary  to  calculate  the 
effect  of  the  mutual  action  of  the  planets  in  chang- 

:  ing  their  orbits.  This  calculation  must  be  made 
with  such  precision  that  there  shall  be  no  doubt  re- 

i  spec  ting  the  results  of  the  theory.  Then  its  results 
must  be  compared  with  the  best  observations.  If 
the  slightest  outstanding  difference  is  established 
there  is  something  wrong  and  the  requirements  of 

1  astronomical   science   are   not   satisfied.     The   com- 

'  plete  solution  of  this  problem  was  entirely  beyond 

207 


SIDE-LIGHTS    ON    ASTRONOMY 

the  power  of  Newton.  When  his  methods  of  re- 
search were  used  he  was  indeed  able  to  show  that 
the  mutual  action  of  the  planets  would  produce  devia- 
tions in  their  motions  of  the  same  general  nature 
with  those  observed,  but  he  was  not  able  to  calculate 
these  deviations  with  numerical  exactness.  His  most 
successful  attempt  in  this  direction  was  perhaps 
made  in  the  case  of  the  moon.  He  showed  that  the 
sun's  disturbing  force  on  this  body  would  produce 
several  inequalities  the  existence  of  which  had  been 
established  by  observation,  and  he  was  also  able  to 
give  a  rough  estimate  of  their  amount,  but  this  was 
as  far  as  his  method  could  go.  A  great  improvement 
had  to  be  made,  and  this  was  effected  not  by  English, 
but  by  continental  mathematicians. 

The  latter  saw,  clearly,  that  it  was  impossible  to 
effect  the  required  solution  by  the  geometrical  mode 
of  reasoning  employed  by  Newton.  The  problem, 
as  it  presented  itself  to  their  minds,  was  to  find 
algebraic  expressions  for  the  positions  of  the  planets 
at  any  time.  The  latitude,  longitude,  and  radius- 
vector  of  each  planet  are  constantly  varying,  but 
they  each  have  a  determined  value  at  each  moment 
of  time.  They  may  therefore  be  regarded  as  func- 
tions of  the  time,  and  the  problem  was  to  express 
these  functions  by  algebraic  formulae  These  alge- 
braic expressions  would  contain,  besides  the  time, 
the  elements  of  the  planetary  orbits  to  be  derived 
from  observation.  The  time  which  we  may  suppose 
to  be  represented  algebraically  by  the  symbol  /,  would 
remain  as  an  unknown  quantity  to  the  end.  What 
the  mathematician  sought  to  do  was  to  present  the 
astronomer  with  a  series  of  algebraic  expressions 
containing  t  as  an  indeterminate  quantity,  and  so, 

208 


THE    ASTRONOMICAL    EPHEMERIS 

by  simply  substituting  for  t  any  year  and  fraction 
of  a  year  whatever — 1600,  1700,  1800,  for  example, 
the  result  would  give  the  latitude,  longitude,  or 
radius- vector  of  a  planet. 

The  problem  as  thus  presented  was  one  of  the 
most  difficult  we  can  perceive  of,  but  the  difficulty 
was  only  an  incentive  to  attacking  it  with  all  the 
greater  energy.  So  long  as  the  motion  was  supposed 
purely  elliptical,  so  long  as  the  action  of  the  planets 
was  neglected ,  the  problem  was  a  simple  one,  requir- 
ing for  its  solution  only  the  analytic  geometry  of  the 
ellipse.  The  real  difficulties  commenced  when  the 
mutual  action  of  the  planets  was  taken  into  account. 
It  is,  of  course,  out  of  the  question  to  give  any  techni- 
cal description  or  analysis  of  the  processes  which 
have  been  invented  for  solving  the  problem;  but  a 
brief  historical  sketch  may  not  be  out  of  place.  A 
complete  and  rigorous  solution  of  the  problem  is 
out  of  the  question — that  is,  it  is  impossible  by  any 
known  method  to  form  an  algebraic  expression  for 
the  co-ordinates  of  a  planet  which  shall  be  absolutely 
exact  in  a  mathematical  sense.  In  whatever  way 
we  go  to  work  the  expression  comes  out  in  the  form 
of  an  infinite  series  of  terms,  each  term  being,  on  the 
whole,  a  little  smaller  as  we  increase  the  number. 
So,  by  increasing  the  number  of  these  various  terms, 
we  can  approach  nearer  and  nearer  to  a  mathematical 
exactness,  but  can  never  reach  it.  The  mathema- 
tician and  astronomer  have  to  be  satisfied  when  they 
have  carried  the  solution  so  far  that  the  neglected 
quantities  are  entirely  beyond  the  powers  of  ob- 
servation. 

Mathematicians  have  worked  upon  the  problem 
in  its  various  phases  for  nearly  two  centuries,  and 

209 


SIDE-LIGHTS    ON    ASTRONOMY 

many  improvements  in  detail  have,  from  time  to 
time,  been  made,  but  no  general  method,  applicable 
to  all  cases,  has  been  devised.  One  plan  is  to  be 
used  in  treating  the  motion  of  the  moon,  another  for 
the  interior  planets,  another  for  Jupiter  and  Saturn, 
another  for  the  minor  planets,  and  so  on.  Under 
these  circumstances  it  will  not  surprise  you  to  learn 
that  our  tables  of  the  celestial  motions  do  not,  in 
general,  correspond  in  accuracy  to  the  present  state 
of  practical  astronomy.  There  is  no  authority  and 
jtio  office  in  the  world  whose  duty  it  is  to  look  after 
the  preparations  of  the  formulae  I  have  described. 
The  work  of  computing  them  has  been  almost  en- 
tirely left  to  individual  mathematicians  whose  taste 
lay  in  that  direction,  and  who  have  sometimes  de- 
voted the  greater  part  of  their  lives  to  calculations 
on  a  single  part  of  the  work.  As  a  striking  instance 
of  this,  the  last  great  work  on  the  Motion  of  the 
Moon,  that  of  Delaunay,  of  Paris,  involved  some 
fifteen  years  of  continuous  hard  labor. 

Hansen,  of  Germany,  who  died  five  years  ago,  de- 
voted almost  his  whole  life  to  investigations  of  this 
class  and  to  the  development  of  new  methods  of  com- 
putation. His  tables  of  the  moon  are  those  now 
used  for  predicting  the  places  of  the  moon  in  all  the 
ephemerides  of  the  world. 

The  only  successful  attempt  to  prepare  systematic 
tables  for  all  the  large  planets  is  that  completed  by 
Le  Verrier  just  before  his  death ;  but  he  used  only  a 
small  fraction  of  the  material  at  his  disposal,  and 
did  not  employ  the  modern  methods,  confining  him- 
self wholly  to  those  invented  by  his  countrymen 
about  the  beginning  of  the  present  century.  For 
him  Jacobi  and  Hansen  had  lived  in  vain, 

210 


THE    ASTRONOMICAL    EPHEMERIS 

The  great  difficulty  which  besets  the  subject  arises 
from  the  fact  that  mathematical  processes  alone  will 
not  give  us  the  position  of  a  planet,  there  being 
seven  unknown  quantities  for  each  planet  which 
must  be  determined  by  observations.  A  planet,  for 
instance,  may  move  in  any  ellipse  whatever,  having 
the  sun  in  one  focus,  and  it  is  impossible  to  tell  what 
ellipse  it  is,  except  from  observation.  The  mean 
motion  of  a  planet,  or  its  period  of  revolution,  can 
only  be  determined  by  a  long  series  of  observations, 
greater  accuracy  being  obtained  the  longer  the  ob- 
servations are  continued.  Before  the  time  of  Brad- 
ley, who  commenced  work  at  the  Greenwich  Ob- 
servatory about  1750,  the  observations  were  so  far 
from  accurate  that  they  are  now  of  no  use  whatever, 
unless  in  exceptional  cases.  Even  Bradley's  ob- 
servations are  in  many  cases  far  less  accurate  than 
those  made  now.  In  consequence,  we  have  not 
heretofore  had  a  sufficiently  extended  series  of  ob- 
servations to  form  an  entirely  satisfactory  theory 
of  the  celestial  motions. 

As  a  consequence  of  the  several  difficulties  and 
drawbacks,  when  the  computation  of  our  ephemeris 
was  started,  in  the  year  1849,  there  were  no  tables 
which  could  be  regarded  as  really  satisfactory  in 
use.  In  the  British  Nautical  Almanac  the  places  of 
the  moon  were  derived  from  the  tables  of  Burck- 
hardt  published  in  the  year  1812.  You  will  under- 
stand, in  a  case  like  this,  no  observations  subsequent 
to  the  issue  of  the  tables  are  made  use  of;  the  place 
of  the  moon  of  any  day,  hour,  and  minute  of  Green- 
wich time,  mean  time,  was  precisely  what  Burck- 
hardt  would  have  computed  nearly  a  half  a  century 
before.  Of  the  tables  of  the  larger  planets  the  latest 

211 


SIDE-LIGHTS    ON    ASTRONOMY 

were  those  of  Bouvard,  published  in  1812,  while  the 
places  of  Venus  were  from  tables  published  by  Linde- 
nau  in  1 8 10.  Of  course  such  tables  did  not  possess 
astronomical  accuracy.  At  that  time,  in  the  case 
of  the  moon,  completely  new  tables  were  constructed 
from  the  results  reached  by  Professor  Airy  in  his  re- 
duction of  the  Greenwich  observations  of  the  moon 
from  1750  to  1830.  These  were  constructed  under 
the  direction  of  Professor  Pierce  and  represented  the 
places  of  the  moon  with  far  greater  accuracy  than 
the  older  tables  of  Burckhardt.  For  the  larger 
planets  corrections  were  applied  to  the  older  tables 
to  make  them  more  nearly  represent  observations  be- 
fore new  ones  were  constructed.  These  corrections, 
however,  have  not  proved  satisfactory,  not  being 
founded  on  sufficiently  thorough  investigations.  In- 
deed, the  operation  of  correcting  tables  by  observa- 
tion, as  we  would  correct  the  dead-reckoning  of  a 
ship,  is  a  makeshift,  the  result  of  which,  must  always 
be  somewhat  uncertain,  and  it  tends  to  destroy  that 
unity  which  is  an  essential  element  of  the  astro- 
nomical ephemeris  designed  for  permanent  future 
use.  The  result  of  introducing  them,  while  no  doubt 
an  improvement  on  the  old  tables,  has  not  been  all 
that  should  be  desired.  The  general  lack  of  unity 
in  the  tables  hitherto  employed  is  such  that  I  can 
only  state  what  has  been  done  by  mentioning  each 
planet  in  detail. 

For  Mercury,  new  tables  were  constructed  by  Pro- 
fessor Winlock,  from  formulae  published  by  Le  Verrier 
in  1846.  These  tables  have,  however,  been  deviating 
from  the  true  motion  of  the  planet,  owing  to  the 
motion  of  the  perihelion  of  Mercury,  subsequently 
discovered  by  Le  Verrier  himself.  They  are  now 

212 


THE    ASTRONOMICAL    EPHEMERIS 

much  less  accurate  than  the  newer  tables  published 
by  Le  Verrier  ten  years  later. 

Of  Venus  new  tables  were  constructed  by  Mr.  Hill 
in  1872.  They  are  more  accurate  than,  any  others, 
being  founded  on  later  data  than  those  of  Le  Verrier, 
and  are  therefore  satisfactory  so  far  as  accuracy  of 
prediction  is  concerned. 

The  place  of  Mars,  Jupiter,  and  Saturn  are  still 
computed  from  the  old  tables,  with  certain  necessary 
corrections  to  make  them  better  represent  observa- 
tions. 

The  places  of  Uranus  and  Neptune  are  derived  from 
new  tables  which  will  probably  be  sufficiently  ac- 
curate for  some  time  to  come. 

For  the  moon,  Pierce's  tables  have  been  employed 
up  to  the  year  1882  inclusive.  Commencing  with  the 
ephemeris  for  the  year  1883,  Hansen's  tables  are 
introduced  with  corrections  to  the  mean  longitude 
founded  on  two  centuries  of  observation. 

With  so  great  a  lack  of  uniformity,  and  in  the  ab- 
sence of  any  existing  tables  which  have  any  other 
element  of  unity  than  that  of  being  the  work  of  the 
same  authors,  it  is  extremely  desirable  that  we  should 
be  able  to  compute  astronomical  ephemerides  from  a 
single  uniform  and  consistent  set  of  astronomical 
|data.  I  hope,  in  the  course  of  years,  to  render  this 

isible. 

When  our  ephemeris  was  first  commenced,  the  cor- 
Irections  applied  to  existing  tables  rendered  it  more 
(accurate  than  any  other.  Since  that  time,  the  intro- 
.uction  into  foreign  ephemerides  of  the  improved 
ibles  of  Le  Verrier  have  rendered  them,  on  the  whole, 
,ther  more  accurate  than  our  own.  In  one  direction, 
lowever,  our  ephemeris  will  hereafter  be  far  ahead 

213 


SIDE-LIGHTS    ON    ASTRONOMY 

of  all  others.  I  mean  in  its  positions  of  the  fixed 
stars.  This  portion  of  it  is  of  particular  importance 
to  us,  owing  to  the  extent  to  which  our  government 
is  engaged  in  the  determination  of  positions  on 'this 
continent,  and  especially  in  our  western  territories. 
Although  the  places  of  the  stars  are  determined  far 
more  easily  than  those  of  the  planets,  the  discussion 
of  star  positions  has  been  in  almost  as  backward  a 
state  as  planetary  positions.  The  errors  of  old  ob- 
servers have  crept  in  and  been  continued  through 
two  generations  of  astronomers.  A  systematic  at- 
tempt has  been  made  to  correct  the  places  of  the 
stars  for  all  systematic  errors  of  this  kind,  and  the 
work  of  preparing  a  catalogue  of  stars  which  shall 
be  completely  adapted  to  the  determination  of  time 
and  longitude,  both  in  the  fixed  observatory  and  in 
the  field,  is  now  approaching  completion.  The  cata- 
logue cannot  be  sufficiently  complete  to  give  places 
of  the  stars  for  determining  the  latitude  by  the 
zenith  telescope,  because  for  such  a  purpose  a  much 
greater  number  of  stars  is  necessary  than  can  be  in- 
corporated in  the  ephemeris. 

From  what  I  have  said,  it  will  be  seen  that  the 
astronomical  tables,  in  general,  do  not  satisfy  the 
scientific  condition  of  completely  representing  ob- 
servations to  the  last  degree  of  accuracy.  Few,  I 
think,  have  an  idea  how  unsystematically  work  of 
this  kind  has  hitherto  been  performed.  Until  very 
lately  the  tables  we  have  possessed  have  been  the 
work  of  one  man  here,  another  there,  and  another 
one  somewhere  else,  each  using  different  methods 
and  different  data.  The  result  of  this  is  that  there 
is  nothing  uniform  and  systematic  among  them,  and 
that  they  have  every  range  of  precision.  This  is  no 

214 


THE    ASTRONOMICAL    EPHEMERIS 

doubt  due  in  part  to  the  fact  that  the  construc- 
tion of  such  tables,  founded  on  the  mass  of  observa- 
tion hitherto  made,  is  entirely  beyond  the  power  of 
any  one  man.  What  is  wanted  is  a  number  of  men 

i  of  different  degrees  of  capacity,  all  co-operating  on 
a  uniform  system,  so  as  to  obtain  a  uniform  result, 
like  the  astronomers  in  a  large  observatory.  The 
Greenwich  Observatory  presents  an  example  of  co- 
operative work  of  this  class  extending  over  more 
than  a  century.  But  it  has  never  extended  its 
operations  far  outside  the  field  of  observation,  re- 
duction, and  comparison  with  existing  tables.  It 
shows  clearly,  from  time  to  time,  the  errors  of  the 
tables  used  in  the  British  Nautical  Almanac,  but 
does  nothing  further,  occasional  investigations  ex- 
cepted,  in  the  way  of  supplying  new  tables.  An  ex- 
ception to  this  is  a  great  work  on  the  theory  of  the 
moon's  motion,  in  which  Professor  Airy  is  now  en- 
gaged. 

It  will  be  understood  that  several  distinct  condi- 
tions not  yet  fulfilled  are  desirable  in  astronomical 
tables ;  one  is  that  each  set  of  tables  shall  be  founded 
on  absolutely  consistent  data;  for  instance,  that  the 
masses  of  the  planets  shall  be  the  same  throughout. 
Another  requirement  is  that  this  data  shall  be  as 
near  the  truth  as  astronomical  data  will  suffice  to 
determine  them.  The  third  is  that  the  results  shall 

(be  correct  in  theory.     That  is,  whether  they  agree 
or  disagree  with  observations,  they  shall  be  such  as 
result  mathematically  from  the  adopted  data. 
Tables  completely  fulfilling  these  conditions  are 

|  still  a  work  of  the  future.     It  is  yet  to  be  seen  whether 

,  such  co-operation  as  is  necessary  to  their  production 
can  be  secured  under  any  arrangement  whatever, 
l*  215 


XIV 
THE    WORLD'S    DEBT    TO    ASTRONOMY 

ASTRONOMY  is  more  intimately  connected  than 
J\  any  other  science  with  the  history  of  mankind. 
While  chemistry,  physics,  and  we  might  say  all 
sciences  which  pertain  to  things  on  the  earth,  are 
comparatively  modern,  we  find  that  contemplative 
men  engaged  in  the  study  of  the  celestial  motions 
even  before  the  commencement  of  authentic  history. 
The  earliest  navigators  of  whom  we  know  must  have 
been  aware  that  the  earth  was  round.  This  fact  was 
certainly  understood  by  the  ancient  Greeks  and 
Egyptians,  as  well  as  it  is  at  the  present  day.  True, 
they  did  not  know  that  the  earth  revolved  on  its 
axis,  but  thought  that  the  heavens  and  all  that  in 
them  is  performed  a  daily  revolution  around  our 
globe,  which  was,  therefore,  the  centre  of  the  universe. 
It  was  the  cynosure,  or  constellation  of  the  Little 
Bear,  by  which  the  sailors  used  to  guide  their  ships 
before  the  discovery  of  the  mariner's  compass.  Thus 
we  see  both  a  practical  and  contemplative  side  to 
astronomy  through  all  history.  The  world  owes  two 
debts  to  that  science:  one  for  its  practical  uses,  and 
the  other  for  the  ideas  it  has  afforded  us  of  the  im- 
mensity of  creation. 

The  practical  uses  of  astronomy  are  of  two  kinds: 
One  relates  to  geography ;  the  other  to  times,  seasons, 

216 


THE    WORLD'S    DEBT    TO    ASTRONOMY 


and  chronology.  Every  navigator  who  sails  long 
out  of  sight  of  land  must  be  something  of  an  astron- 
omer. His  compass  tells  him  where  are  east,  west, 
north,  and  south,  but  it  gives  him  no  information  as 
to  where  on  the  wide  ocean  he  may  be,  or  whither  the 
currents  may  be  carrying  him.  Even  with  the  swift- 
est modern  steamers  it  is  not  safe  to  trust  to  the  com- 
pass in  crossing  the  Atlantic.  A  number  of  years 
ago  the  steamer  City  of  Washington  set  out  on  her 
usual  voyage  from  Liverpool  to  New  York.  By  rare 
bad  luck  the  weather  was  stormy  or  cloudy  during 
her  whole  passage,  so  that  the  captain  could  not  get 
a  sight  on  the  sun,  and  therefore  had  to  trust  to  his 
compass  and  his  log-line,  the  former  telling  him  in 
what  direction  he  had  steamed,  and  the  latter  how 
fast  he  was  going  each  hour.  The  result  was  that 
the  ship  ran  ashore  on  the  coast  of  Nova  Scotia, 
when  the  captain  thought  he  was  approaching  Nan- 
tucket. 

Not  only  the  navigator  but  the  surveyor  in  the 
western  wilds  must  depend  on  astronomical  observa- 
tions to  learn  his  exact  position  on  the  earth's  sur- 
face, or  the  latitude  and  longitude  of  the  camp  which 
he  occupies.  He  is  able  to  do  this  because  the  earth 
is  round,  and  the  direction  of  the  plumb-line  not 
exactly  the  same  at  any  two  places.  Let  us  suppose 
that  the  earth  stood  still,  so  as  not  to  revolve  on  its 
axis  at  all.  Then  we  should  always  see  the  stars  at 
rest  and  the  star  which  was  in  the  zenith  of  any 
place,  say  a  farm-house  in  New  York,  at  any  time, 
would  be  there  every  night  and  every  hour  of  the 
year.  Now  the  zenith  is  simply  the  point  from  which 
the  plumb-line  seems  to  drop.  Lie  on  the  ground; 
hang  a  plummet  above  your  head,  sight  on  the  line 

217 


SIDE-LIGHTS    ON    ASTRONOMY 

with  one  eye,  and  the  direction  of  the  sight  will  be 
the  zenith  of  your  place.  Suppose  the  earth  was  still, 
and  a  certain  star  was  at  your  zenith.  Then  if  you 
went  to  another  place  a  mile  away,  the  direction  of 
the  plumb-line  would  be  slightly  different.  The 
change  would,  indeed,  be  very  small,  so  small  that 
you  could  not  detect  it  by  sighting  with  the  plumb- 
line.  But  astronomers  and  surveyors  have  vastly 
more  accurate  instruments  than  the  plumb-line  and 
the  eye,  instruments  by  which  a  deviation  that  the 
unaided  eye  could  not  detect  can  be  seen  and  meas- 
ured. Instead  of  the  plumb-line  they  use  a  spirit- 
level  or  a  basin  of  quicksilver.  The  surface  of  quick- 
silver is  exactly  level  and  so  at  right  angles  to  the 
true  direction  of  the  plumb-line  or  the  force  of  gravity. 
Its  direction  is  therefore  a  little  different  at  two  dif- 
ferent places  on  the  surface,  and  the  change  can  be 
measured  by  its  effect  on  the  apparent  direction  of 
a  star  seen  by  reflection  from  the  surface. 

It  is  true  that  a  considerable  distance  on  the  earth's 
surface  will  seem  very  small  in  its  effect  on  the  posi- 
tion of  a  star.  Suppose  there  were  two  stars  in  the 
heavens,  the  one  in  the  zenith  of  the  place  where  you 
now  stand,  and  the  other  in  the  zenith  of  a  place  a 
mile  away.  To  the  best  eye  unaided  by  a  telescope 
those  two  stars  would  look  like  a  single  one.  But  let 
the  two  places  be  five  miles  apart,  and  the  eye  could 
see  that  there  were  two  of  them.  A  good  telescope 
could  distinguish  between  two  stars  corresponding 
to  places  not  more  than  a  hundred  feet  apart.  The 
most  exact  measurements  can  determine  distances 
ranging  from  thirty  to  sixty  feet.  If  a  skilful  as- 
tronomical observer  should  mount  a  telescope  on  your 
premises,  and  determine  his  latitude  by  observations 

218 


THE    WORLD'S    DEBT    TO    ASTRONOMY 

on  two  or  three  evenings,  and  then  you  should  try  to 
trick  him  by  taking  up  the  instrument  and  putting 
it  at  another  point  one  hundred  feet  north  or  south, 
he  would  find  out  that  something  was  wrong  by  a 
single  night's  work. 

Within  the  past  three  years  a  wobbling  of  the 
earth's  axis  has  been  discovered,  which  takes  place 
within  a  circle  thirty  feet  in  radius  and  sixty  feet  in 
diameter.  Its  effect  was  noticed  in  astronomical 
observations  many  years  ago,  but  the  change  it  pro- 
duced was  so  small  that  men  could  not  find  out  what 
the  matter  was.  The  exact  nature  and  amount  of 
the  wobbling  is  a  work  of  the  exact  astronomy  of  the 
present  time. 

We  cannot  measure  across  oceans  from  island  to 

island.      Until   a    recent    time  we    have    not    even 

measured  across  the  continent,  from  New  York  to 

San  Francisco,  in  the  most  precise  way.     Without 

astronomy  we  should  know  nothing  of  the  distance 

i  between  New  York  and  Liverpool,   except  by  the 

time  which  it  took  steamers  to  run  it,  a  measure 

which  would  be  very  uncertain  indeed.     But  by  the 

aid  of  astronomical  observations  and  the  Atlantic 

cables  the  distance  is  found  within  a  few  hundred 

yards.     Without  astronomy  we  could  scarcely  make 

an  accurate  map  of  the  United  States,   except  at 

I  enormous  labor  and  expense,  and  even  then  we  could 

j  not  be  sure  of  its  correctness.     But  the  practical  as- 

|  tronomer  being  able  to  determine  his  latitude  and 

longitude  within   fifty   yards,    the   positions   of  the 

i  principal  points  in  all  great  cities  of  the  country  are 

known,  and  can  be  laid  down  on  maps. 

The  world  has  always  had  to  depend  on  astronomy 
for  all  its  knowledge  concerning  times  and  seasons. 

219 


SIDE-LIGHTS    ON    ASTRONOMY 

The  changes  of  the  moon  gave  us  the  first  month, 
and  the  year  completes  its  round  as  the  earth  travels 
in  its  orbit.  The  results  of  astronomical  observation 
are  for  us  condensed  into  almanacs,  which  are  now  in 
such  universal  use  that  we  never  think  of  their  as- 
tronomical origin.  But  in  ancient  times  people  had 
no  almanacs,  and  they  learned  the  time  of  year,  or 
the  number  of  days  in  the  year,  by  observing  the 
time  when  Sirius  or  some  other  bright  star  rose  or  set 
with  the  sun,  or  disappeared  from  view  in  the  sun's 
rays.  At  Alexandria,  in  Egypt,  the  length  of  the  year 
was  determined  yet  more  exactly  by  observing  when 
the  sun  rose  exactly  in  the  east  and  set  exactly  in  the 
west,  a  date  which  fixed  the  equinox  for  them  as  for 
us.  More  than  seventeen  hundred  years  ago,  Ptolemy, 
the  great  author  of  The  Almagest,  had  fixed  the  length 
of  the  year  to  within  a  very  few  minutes.  He  knew 
it  was  a  little  less  than  365^  days.  The  dates  of 
events  in  ancient  history  depend  very  largely  on  the 
chronological  cycles  of  astronomy.  Eclipses  of  the 
sun  and  moon  sometimes  fixed  the  date  of  great 
events,  and  we  learn  the  relation  of  ancient  calendars 
to  our  own  through  the  motions  of  the  earth  and 
moon,  and  can  thus  measure  out  the  years  for  the 
events  in  ancient  history  on  the  same  scale  that  we 
measure  out  our  own. 

At  the  present  day,  the  work  of  the  practical  as- 
tronomer is  made  use  of  in  our  daily  life  throughout 
the  whole  country  in  yet  another  way.  Our  fore- 
fathers had  to  regulate  their  clocks  by  a  sundial,  or 
perhaps  by  a  mark  at  the  corner  of  the  house,  which 
showed  where  the  shadow  of  the  house  fell  at  noon. 
Very  rude  indeed  was  this  method;  and  it  was  un- 
certain for  another  reason.  It  is  not  always  exactly 

220 


THE    WORLD'S    DEBT    TO    ASTRONOMY 

twenty-four  hours  between  two  noons  by  the  sun. 
Sometimes  for  two  or  three  months  the  sun  will 
make  it  noon  earlier  and  earlier  every  day;  and 
during  several  other  months  later  and  later  every 
day.  The  result  is  that,  if  a  clock  is  perfectly  regu- 
lated, the  sun  will  be  sometimes  a  quarter  of  an  hour 
behind  it,  and  sometimes  nearly  the  same  amount 
before  it.  Any  effort  to  keep  the  clock  in  accord 
with  this  changing  sun  was  in  vain,  and  so  the  time 
of  day  was  always  uncertain. 

Now,  however,  at  some  of  the  principal  observa- 
tories of  the  country  astronomical  observations  are 
made  on  every  clear  night  for  the  express  purpose  of 
regulating  an  astronomical  clock  with  the  greatest 
exactness.  Every  day  at  noon  a  signal  is  sent  to 
various  parts  of  the  country  by  telegraph,  so  that  all 
operators  and  railway  men  who  hear  that  signal  can 
set  their  clock  at  noon  within  two  or  three  seconds. 
People  who  live  near  railway  stations  can  thus  get 
their  time  from  it,  and  so  exact  time  is  diffused  into 
every  household  of  the  land  which  is  at  all  near  a 
railway  station,  without  the  trouble  of  watching  the 
sun.  Thus  increased  exactness  is  given  to  the  time 
on  all  our  railroads,  increased  safety  is  obtained,  and 
great  loss  of  time  saved  to  every  one.  If  we  esti- 
mated the  money  value  of  this  saving  alone  we 
should  no  doubt  find  it  to  be  greater  than  all  that 
our  study  of  astronomy  costs. 

It  must  therefore  be  conceded  that,  on  the  whole, 
astronomy  is  a  science  of  more  practical  use  than  one 
would  at  first  suppose.  To  the  thoughtless  man,  the 
stars  seem  to  have  very  little  relation  to  his  daily  life ; 
they  might  be  forever  hid  from  view  without  his  being 
the  worse  for  it.  He  wonders  what  object  men  can 

221 


SIDE-LIGHTS    ON    ASTRONOMY 

have  in  devoting  themselves  to  the  study  of  the  mo- 
tions or  phenomena  of  the  heavens.  But  the  more 
he  looks  into  the  subject,  and  the  wider  the  range 
which  his  studies  include,  the  more  he  will  be  im- 
pressed with  the  great  practical  usefulness  of  the 
science  of  the  heavens.  And  yet  I  think  it  would 
be  a  serious  error  to  say  that  the  world's  greatest 
debt  to  astronomy  was  owing  to  its  usefulness  in 
surveying,  navigation,  and  chronology.  The  more 
enlightened  a  man  is,  the  more  he  will  feel  that 
what  makes  his  mind  what  it  is,  and  gives  him 
the  ideas  of  himself  and  creation  which  he  possess- 
es, is  more  important  than  that  which  gains  him 
wealth.  I  therefore  hold  that  the  world's  greatest 
debt  to  astronomy  is  that  it  has  taught  us  what  a 
great  thing  creation  is,  and  what  an  insignificant 
part  of  the  Creator's  work  is  this  earth  on  which  we 
dwell,  and  everything  that  is  upon  it.  That  space  is 
infinite,  that  wherever  we  go  there  is  a  farther  still 
beyond  it,  must  have  been  accepted  as  a  fact  by  all 
men  who  have  thought  of  the  subject  since  men  be- 
gan to  think  at  all.  But  it  is  very  curious  how  hard 
even  the  astronomers  found  it  to  believe  that  creation 
is  as  large  as  we  now  know  it  to  be.  The  Greeks  had 
their  gods  on  or  not  very  far  above  Olympus,  which 
was  a  sort  of  footstool  to  the  heavens.  Sometimes 
they  tried  to  guess  how  far  it  probably  was  from  the 
vault  of  heaven  to  the  earth,  and  they  had  a  myth 
as  to  the  time  it  took  Vulcan  to  fall.  Ptolemy  knew 
that  the  moon  was  about  thirty  diameters  of  the 
earth  distant  from  us,  and  he  knew  that  the  sun  was 
many  times  farther  than  the  moon;  he  thought  it 
about  twenty  times  as  far,  but  could  not  be  sure. 
We  know  that  it  is  nearly  four  hundred  times  as  far. 

222 


THE    WORLD'S    DEBT    TO    ASTRONOMY 

\Vhen  Copernicus  propounded  the  theory  that  the 
earth  moved  around  the  sun,  and  not  the  sun  around 
the  earth,  he  was  able  to  fix  the  relative  distances  of 
the  several  planets,  and  thus  make  a  map  of  the  solar 
system.  But  he  knew  nothing  about  the  scale  of  this 
map.  He  knew,  for  example,  that  Venus  was  a  little 
more  than  two-thirds  the  distance  of  the  earth  from 
the  sun,  and  that  Mars  was  about  half  as  far  again 
as  the  earth,  Jupiter  about  five  times,  and  Saturn 
about  ten  times ;  but  he  knew  nothing  about  the  dis- 
tance of  any  one  of  them  from  the  sun.  He  had  his 
map  all  right,  but  he  could  not  give  any  scale  of  miles 
or  any  other  measurements  upon  it.  The  astrono- 
mers who  first  succeeded  him  found  that  the  distance 
was  very  much  greater  than  had  formerly  been  sup- 
posed; that  it  was,  in  fact,  for  them  immeasurably 
great,  and  that  was  all  they  could  say  about  it. 

The  proofs  which  Copernicus  gave  that  the  earth 
revolved  around  the  sun  were  so  strong  that  none 
could  well  doubt  them.     And  yet  there  was  a  diffi- 
culty in  accepting  the  theory  which  seemed  insuper- 
able.    If  the  earth  really  moved  in  so  immense  an 
orbit  as  it  must,  then  the  stars  would  seem  to  move 
j  in  the  opposite  direction,  just  as,  if  you  were  in  a 
j  train  that  is  shunting  off  cars  one  after  another,  as 
I  the  train  moves  back  and  forth  you  see  its  motion  in 
!  the  opposite  motion  of  every  object  around  you.     If 
j  then  the  earth  at  one  side  of  its  orbit  was  exactly 
i  between  two  stars,  when  it  moved  to  the  other  side 
!  of  its  orbit  it  would  not  be  in  a  line  between  them, 
but  each  star  would  have  seemed  to  move  in  the  op- 
posite direction. 

For  centuries  astronomers  made  the  most  exact 
observations  that  they  were  able  without  having  suc- 

223 


SIDE-LIGHTS    ON    ASTRONOMY 

ceeded  in  detecting  any  such  apparent  motion  among 
the  stars.  Here  was  a  mystery  which  they  could  not 
solve.  Either  the  Copernican  system  was  not  true, 
after  all,  and  the  earth  did  not  move  in  an  orbit,  or 
the  stars  were  at  such  immense  distances  that  the 
whole  immeasurable  orbit  of  the  earth  is  a  mere 
point  in  comparison.  Philosophers  could  not  believe 
that  the  Creator  would  waste  room  by  allowing  the 
inconceivable  spaces  which  appeared  to  lie  between 
our  system  and  the  fixed  stars  to  remain  unused,  and 
so  thought  there  must  be  something  wrong  in  the 
theory  of  the  earth's  motion. 

Not  until  the  nineteenth  century  was  well  in  prog- 
ress did  the  most  skilful  observers  of  their  time, 
Bessel  and  Struve,  having  at  command  the  most  re- 
fined instruments  which  science  was  then  able  to 
devise,  discover  the  reality  of  the  parallax  of  the 
stars,  and  show  that  the  nearest  of  these  bodies 
which  they  could  find  was  more  than  400,000  times 
as  far  as  the  93,000,000  of  miles  which  separate 
the  earth  from  the  sun.  During  the  half -century 
and  more  which  has  elapsed  since  this  discovery, 
astronomers  have  been  busily  engaged  in  fathom- 
ing the  heavenly  depths.  The  nearest  star  they 
have  been  able  to  find  is  about  280,000  times  the 
sun's  distance.  A  dozen  or  a  score  more  are  within 
1,000,000  times  that  distance.  Beyond  this  all  is 
unfathomable  by  any  sounding  -  line  yet  known  to 
man. 

The  results  of  these  astronomical  measures  are 
stupendous  beyond  conception.  No  mere  statement 
in  numbers  conveys  any  idea  of  it.  Nearly  all  the 
brighter  stars  are  known  to  be  flying  through  space 
at  speeds  which  generally  range  between  ten  and 

224 


THE    WORLD'S    DEBT    TO    ASTRONOMY 

forty  or  fifty  miles  per  second,  some  slower  and 
some  swifter,  even  up  to  one  or  two  hundred  miles 
a  second.  Such  a  speed  would  carry  us  across  the 
Atlantic  while  we  were  reading  two  or  three  of  these 
sentences.  These  motions  take  place  some  in  one 
direction  and  some  in  another.  Some  of  the  stars 
are  coming  almost  straight  towards  us.  Should  they 
reach  us,  and  pass  through  our  solar  system,  the 

;  result  would  be  destructive  to  our  earth,  and  perhaps 

|  to  our  sun. 

Are  we  in  any  danger?  No,  because,  however 
madly  they  may  come,  whether  ten,  twenty,  or  one 
hundred  miles  per  second,  so  many  millions  of  years 
must  elapse  before  they  reach  us  that  we  need  give 
ourselves  no  concern  in  the  matter.  Probably  none 
of  them  are  coming  straight  to  us;  their  course 
deviates  just  a  hair's-breadth  from  our  system,  but 
that  hair's-breadth  is  so  large  a  quantity  that  when 
the  millions  of  years  elapse  their  course  will  lie  on 
one  side  or  the  other  of  our  system  and  they  will  do 
no  harm  to  our  planet;  just  as  a  bullet  fired  at  an 
insect  a  mile  away  would  be  nearly  sure  to  miss  it 
in  one  direction  or  the  other. 

Our  instrument  makers  have  constructed  telescopes 

;more  and  more  powerful,  and  with  these  the  whole 
number  of  stars  visible  is  carried  up  into  the  millions, 

;  say  perhaps  to  fifty  or  one  hundred  millions .  For  aught 

I  we  know  every  one  of  those  stars  may  have  planets 

1  like  our  own  circling  round  it,  and  these  planets  may 
be  inhabited  by  beings  equal  to  ourselves.  To  sup- 
pose that  our  globe  is  the  only  one  thus  inhabited 
is  something  so  unlikely  that  no  one  could  expect 

'it.     It  would  be  very  nice  to  know  something  about 

t1-^  people  who  may  inhabit  these  bodies,  but  we 
„, 


SIDE-LIGHTS     ON    ASTRONOMY 

must  await  our  translation  to  another  sphere  before 
we  can  know  anything  on  the  subject.  Meanwhile, 
we  have  gained  what  is  of  more  value  than  gold  or 
silver;  we  have  learned  that  creation  transcends  all 
our  conceptions,  and  our  ideas  of  its  Author  are  en- 
larged accordingly. 


XV 

AN   ASTRONOMICAL    FRIENDSHIP 

HPHERE  are  few  men  with  whom  I  would  like  so 
1  well  to  have  a  quiet  talk  as  with  Father  Hell.  I 
have  known  more  important  and  more  interesting 
men,  but  none  whose  acquaintance  has  afforded  me  a 
serener  satisfaction,  or  imbued  me  with  an  ampler 
measure  of  a  feeling  that  I  am  candid  enough  to  call 
self-complacency.  The  ties  that  bind  us  are  peculiar. 
When  I  call  him  my  friend,  I  do  not  mean  that  we 
ever  hobnobbed  together.  But  if  we  are  in  sym- 
pathy, what  matters  it  that  he  was  dead  long  before 
I  was  born,  that  he  lived  in  one  century  and  I  in 
another?  Such  differences  of  generation  count  for 
little  in  the  brotherhood  of  astronomy,  the  work  of 
whose  members  so  extends  through  all  time  that  one 
might  well  forget  that  he  belongs  to  one  century  or 

!to  another. 

Father  Hell  was  an  astronomer.     Ask  not  whether 
he  was  a  very  great  one,  for  in  our  science  we  have  no 

<  infallible  gauge  by  which  we  try  men  and  measure 

'their  stature.  He  was  a  lover  of  science  and  an  in- 
defatigable worker,  and  he  did  what  in  him  lay  to 
advance  our  knowledge  of  the  stars.  Let  that  suf- 
fice. I  love  to  fancy  that  in  some  other  sphere, 

|  either  within  this  universe  of  ours  or  outside  of  it, 
all  who  have  successfully  done  this  may  some  time 

227 


SIDE-LIGHTS    ON    ASTRONOMY 

gather  and  exchange  greetings.  Should  this  come 
about  there  will  be  a  few — Hipparchus  and  Ptolemy, 
Copernicus  and  Newton,  Galileo  and  Herschel  —  to 
be  surrounded  by  admiring  crowds.  But  these  men 
will  have  as  warm  a  grasp  and  as  kind  a  word  for  the 
humblest  of  their  followers,  who  has  merely  discov- 
ered a  comet  or  catalogued  a  nebula,  as  for  the  more 
brilliant  of  their  brethren. 

My  friend  wrote  the  letters  S.  J.  after  his  name. 
This  would  indicate  that  he  had  views  and  tastes 
which,  in  some  points,  were  very  different  from  my 
own.  But  such  differences  mark  no  dividing  line  in 
the  brotherhood  of  astronomy.  My  testimony  would 
count  for  nothing  were  I  called  as  witness  for  the 
prosecution  in  a  case  against  the  order  to  which  my 
friend  belonged.  The  record  would  be  very  short: 
Deponent  saith  that  he  has  at  various  times  known 
sundry  members  of  the  said  order;  and  that  they 
were  lovers  of  sound  learning,  devoted  to  the  dis- 
covery and  propagation  of  knowledge;  and  further 
deponent  saith  not. 

If  it  be  true  that  an  undevout  astronomer  is  mad, 
then  was  Father  Hell  the  sanest  of  men.  In  his 
diary  we  find  entries  like  these:  " Benedicente  Deo,  I 
observed  the  Sun  on  the  meridian  to-day.  .  .  .  Deo 
quoque  benedicente,  I  to-day  got  corresponding  alti- 
tudes of  the  Sun's  upper  limb."  How  he  maintained 
the  simplicity  of  his  faith  in  the  true  spirit  of  the 
modern  investigator  is  shown  by  his  proceedings 
during  a  momentous  voyage  along  the  coast  of  Nor- 
way, of  which  I  shall  presently  speak.  He  and  his 
party  were  passengers  on  a  Norwegian  vessel.  For 
twelve  consecutive  days  they  had  been  driven  about 
by  adverse  storms,  threatened  with  shipwreck  on 

228 


AN    ASTRONOMICAL    FRIENDSHIP 

stony  cliffs,  and  finally  compelled  to  take  refuge  in 
a  little  bay,  with  another  ship  bound  in  the  same 
direction,  there  to  wait  for  better  weather. 

Father  Hell  was  philosopher  enough  to  know  that 
unusual  events  do  not  happen  without  cause.  Per- 
haps he  would  have  undergone  a  week  of  storm  with- 
out its  occurring  to  him  to  investigate  the  cause  of 
such  a  bad  spell  of  weather.  But  when  he  found  the 
second  week  approaching  its  end  and  yet  no  sign  of 
the  sun  appearing  or  the  wind  abating,  he  was  satis- 
fied that  something  must  be  wrong.  So  he  went  to 
work  in  the  spirit  of  the  modern  physician  who, 
when  there  is  a  sudden  outbreak  of  typhoid  fever, 
looks  at  the  wells  and  examines  their  water  with  the 
miscroscope  to  find  the  microbes  that  must  be  lurk- 
ing somewhere.  He  looked  about,  and  made  care- 
ful inquiries  to  find  what  wickedness  captain  and 
crew  had  been  guilty  of  to  bring  such  a  punishment. 
Success  soon  rewarded  his  efforts.  The  King  of 
Denmark  had  issued  a  regulation  that  no  fish  or  oil 
should  be  sold  along  the  coast  except  by  the  regular 
dealers  in  those  articles.  And  the  vessel  had  on 
board  contraband  fish  and  blubber,  to  be  disposed 
of  in  violation  of  this  law. 

The  astronomer  took  immediate  and  energetic 
measures  to  insure  the  public  safety.  He  called  the 
crew  together,  admonished  them  of  their  sin,  the 
suffering  they  were  bringing  on  themselves,  and  the 
necessity  of  getting  back  to  their  families.  He  ex- 
horted them  to  throw  the  fish  overboard,  as  the  only 
measure  to  secure  their  safety.  In  the  goodness  of 
his  heart,  he  even  offered  to  pay  the  value  of  the 
jettison  as  soon  as  the  vessel  reached  Drontheim. 

But  the  descendants  of  the  Vikings  were  stupid 

229 


SIDE-LIGHTS    ON    ASTRONOMY 

and  unenlightened  men — "  educatione  sua  et  professione 
homines  eras sis simi" —  and  would  not  swallow  the 
medicine  so  generously  offered.  They  claimed  that, 
as  they  had  bought  the  fish  from  the  Russians,  their 
proceedings  were  quite  lawful.  As  for  being  paid 
to  throw  the  fish  overboard,  they  must  have  spot  cash 
in  advance  or  they  would  not  do  it. 

After  further  fruitless  conferences,  Father  Hell 
determined  to  escape  the  danger  by  transferring  his 
party  to  the  other  vessel.  They  had  not  more  than 
got  away  from  the  wicked  crew  than  Heaven  began 
to  smile  on  their  &ct—"factum  comprobare  Dens  ipse 
videtur" — -the  clouds  cleared  away,  the  storm  ceased 
to  rage,  and  they  made  their  voyage  to  Copenhagen 
under  sunny  skies.  I  regret  to  say  that  the  narrative 
is  silent  as  to  the  measure  of  storm  subsequently 
awarded  to  the  homines  crassissimi  of  the  forsaken 
vessel. 

For  more  than  a  century  Father  Hell  had  been  a 
well-known  figure  in  astronomical  history.  His  celeb- 
rity was  not,  however,  of  such  a  kind  as  the  Royal 
Astronomer  of  Austria  that  he  was  ought  to  enjoy. 
A  not  unimportant  element  in  his  fame  was  a  sus- 
picion of  his  being  a  black  sheep  in  the  astronomical 
flock.  He  got  under  this  cloud  through  engaging  in 
a  trying  and  worthy  enterprise.  On  June  3,  1769, 
an  event  occurred  which  had  for  generations  been 
anticipated  with  the  greatest  interest  by  the  whole 
astronomical  world.  This  was  a  transit  of  Venus 
over  the  disk  of  the  sun.  Our  readers  doubtless  know 
that  at  that  time  such  a  transit  afforded  the  most 
accurate  method  known  of  determining  the  distance 
of  the  earth  from  the  sun.  To  attain  this  object,  par- 
ties were  sent  to  the  most  widely  separated  parts  of 

230 


AN    ASTRONOMICAL    FRIENDSHIP 

the  globe,  not  only  over  wide  stretches  of  longitude, 
but  as  near  as  possible  to  the  two  poles  of  the  earth. 
One  of  the  most  favorable  and  important  regions  of 
observation  was  Lapland,  and  the  King  of  Denmark, 
to  whom  that  country  then  belonged,  interested  him- 
self in  getting  a  party  sent  thither.  After  a  care- 
ful survey  of  the  field  he  selected  Father  Hell,  Chief 
of  the  Observatory  at  Vienna,  and  well  known  as 
editor  and  publisher  of  an  annual  ephemeris,  in  which 
the  movements  and  aspects  of  the  heavenly  bodies 
were  predicted .  The  astronomer  accepted  the  mission 
and  undertook  what  was  at  that  time  a  rather  hazard- 
ous voyage.  His  station  was  at  Vardo  in  the  region 
of  the  North  Cape.  What  made  it  most  advanta- 
geous for  the  purpose  was  its  being  situated  several 
degrees  within  the  Arctic  Circle,  so  that  on  the  date 
of  the  transit  the  sun  did  not  set.  The  transit  began 
when  the  sun  was  still  two  or  three  hours  from  his 
midnight  goal,  and  it  ended  nearly  an  equal  time 
afterwards.  The  party  consisted  of  Hell  himself,  his 
friend  and  associate,  Father  Sajnovics,  one  Dominus 
Borgrewing,  of  whom  history,  so  far  as  I  know,  says 
nothing  more,  and  an  humble  individual  who  in  the 
•record  receives  no  other  designation  than  "  Familias." 
This  implies,  we  may  suppose,  that  he  pitched  the 
tent  and  made  the  coffee.  If  he  did  nothing  but  this 
we  might  pass  him  over  in  silence.  But  we  learn 
;that  on  the  day  of  the  transit  he  stood  at  the  clock 
:and  counted  the  all-important  seconds  while  the  ob- 
servations were  going  on. 

The  party  was  favored  by  cloudless  weather,  and 

made  the  required  observations  with  entire  success. 

They  returned  to  Copenhagen,  and  there  Father  Hell 

remained  to  edit  and  publish  his  work.     Astronomers 

'6  231 


SIDE-LIGHTS    ON    ASTRONOMY 

were  naturally  anxious  to  get  the  results,  and  showed 
some  impatience  when  it  became  known  that  Hell 
refused  to  announce  them  until  they  were  all  reduced 
and  printed  in  proper  form  under  the  auspices  of  his 
royal  patron.  While  waiting,  the  story  got  abroad 
that  he  was  delaying  the  work  until  he  got  the  results 
of  observations  made  elsewhere,  in  order  to  ''doctor" 
his  own  and  make  them  fit  in  with  the  others.  One 
went  so  far  as  to  express  a  suspicion  that  Hell  had 
not  seen  the  transit  at  all,  owing  to  clouds,  and  that 
what  he  pretended  to  publish  were  pure  fabrications. 
But  his  book  came  out  in  a  few  months  in  such  good 
form  that  this  suspicion  was  evidently  groundless. 
Still,  the  fears  that  the  observations  were  not  genuine 
were  not  wholly  allayed,  and  the  results  derived  from 
them  were,  in  consequence,  subject  to  some  doubt. 
Hell  himself  considered  the  reflections  upon  his  in- 
tegrity too  contemptible  to  merit  a  serious  reply.  It 
is  said  that  he  wrote  to  some  one  offering  to  exhibit 
his  journal  free  from  interlineations  or  erasures,  but 
it  does  not  appear  that  there  is  any  sound  authority 
for  this  statement.  What  is  of  some  interest  is  that 
he  published  a  determination  of  the  parallax  of  the 
sun  based  on  the  comparison  of  his  own  observations 
with  those  made  at  other  stations.  The  result  was 
8". 70.  It  was  then,  and  long  after,  supposed  that 
the  actual  value  of  the  parallax  was  about  8". 50, 
and  the  deviation  of  Hell's  result  from  this  was  con- 
sidered to  strengthen  the  doubt  as  to  the  correctness 
of  his  work.  It  is  of  interest  to  learn  that,  by  the 
most  recent  researches,  the  number  in  question  must 
be  between  8". 75  and  8". 80,  so  that  in  reality  Hell's 
computations  came  nearer  the  truth  than  those  gen- 
erally current  during  the  century  following  his  work. 

232 


AN  ASTRONOMICAL  FRIENDSHIP 

Thus  the  matter  stood  for  sixty  years  after  the 
transit,  and  for  a  generation  after  Father  Hell  had 
gone  to  his  rest.  About  1830  it  was  found  that  the 
original  journal  of  his  voyage,  containing  the  record 
of  his  work  as  first  written  down  at  the  station,  was 
still  preserved  at  the  Vienna  Observatory.  Littrow, 
then  an  astronomer  at  Vienna,  made  a  critical  exam- 
ination of  this  record  in  order  to  determine  whether 
it  had  been  tampered  with.  His  conclusions  were 
published  in  a  little  book  giving  a  transcript  of  the 
journal,  a  facsimile  of  the  most  important  entries, 
and  a  very  critical  description  of  the  supposed  altera- 
tions made  in  them.  He  reported  in  substance  that 
the  original  record  had  been  so  tampered  with  that 
it  was  impossible  to  decide  whether  the  observations 
as  published  were  genuine  or  not.  The  vital  figures, 
those  which  told  the  times  when  Venus  entered  upon 
the  sun,  had  been  erased,  and  rewritten  with  blacker 
ink.  This  might  well  have  been  done  after  the  party 
returned  to  Copenhagen.  The  case  against  the  ob- 
server seemed  so  well  made  out  that  professors  of  as- 
tronomy gave  their  hearers  a  lesson  in  the  value  of 
truthfulness,  by  telling  them  how  Father  Hell  had 
destroyed  what  might  have  been  very  good  observa- 
tions by  trying  to  make  them  appear  better  than  they 
really  were. 

In  1883  I  paid  a  visit  to  Vienna  for  the  purpose  of 
examining  the  great  telescope  which  had  just  been 
mounted  in  the  observatory  there  by  Grubb,  of  Dub- 
lin. The  weather  was  so  unfavorable  that  it  was 
necessary  to  remain  two  weeks,  waiting  for  an  op- 
portunity to  see  the  stars.  One  evening  I  visited 
the  theatre  to  see  Edwin  Booth,  in  his  celebrated 
tour  over  the  Continent,  play  King  Lear  to  the  ap- 

233 


SIDE-LIGHTS    ON    ASTRONOMY 

plauding  Viennese.  But  evening  amusements  can- 
not be  utilized  to  kill  time  during  the  day.  Among 
the  works  I  had  projected  was  that  of  rediscussing 
all  the  observations  made  on  the  transits  of  Venus 
which  had  occurred  in  1761  and  1769,  by  the  light  of 
modern  discovery.  As  I  have  already  remarked, 
Hell's  observations  were  among  the  most  important 
made,  if  they  were  only  genuine.  So,  during  my  al- 
most daily  visits  to  the  observatory,  I  asked  per- 
mission of  the  director  to  study  Hell's  manuscript, 
which  was  deposited  in  the  library  of  the  institution. 
Permission  was  freely  given,  and  for  some  days  I 
pored  over  the  manuscript.  It  is  a  very  common 
experience  in  scientific  research  that  a  subject  which 
seems  very  unpromising  when  first  examined  may 
be  found  more  and  more  interesting  as  one  looks 
further  into  it.  Such  was  the  case  here.  For  some 
time  there  did  not  seem  any  possibility  of  deciding 
the  question  whether  the  record  was  genuine.  But 
every  time  I  looked  at  it  some  new  point  came  to 
light.  I  compared  the  pages  with  Littrow's  pub- 
lished description  and  was  struck  by  a  seeming  want 
of  precision,  especially  when  he  spoke  of  the  ink  with 
which  the  record  had  been  made.  Erasers  were 
doubtless  unknown  in  those  days — at  least  our  as- 
tronomer had  none  on  his  expedition — so  when  he 
found  he  had  written  the  wrong  word  he  simply 
wiped  the  place  off  with,  perhaps,  his  finger  and  wrote 
what  he  wanted  to  say.  In  such  a  case  Littrow  de- 
scribed the  matter  as  erased  and  new  matter  written. 
When  the  ink  flowed  freely  from  the  quill  pen  it  was 
a  little  dark.  Then  Littrow  said  a  different  kind  of 
ink  had  been  used,  probably  after  he  had  got  back 
from  his  journey.  On  the  other  hand,  there  was  a 

234 


AN    ASTRONOMICAL    FRIENDSHIP 

very  singular  case  in  which  there  had  been  a  sub- 
sequent interlineation  in  ink  of  quite  a  different  tint, 
which  Littrow  said  nothing  about.  This  seemed  so 
curious  that  I  wrote  in  my  notes  as  follows: 

"That  Littrow,  in  arraying  his  proofs-  of  Hell's 
forgery,  should  have  failed  to  dwell  upon  the  obvious 
difference  between  this  ink  and  that  with  which  the 
alterations  were  made  leads  me  to  suspect  a  defect 
in  his  sense  of  color. " 

The  more  I  studied  the  description  and  the  manu- 
script the  stronger  this  impression  became.  Then  it 
occurred  to  me  to  inquire  whether  perhaps  such  could 
have  been  the  case.  So  I  asked  Director  Weiss 
whether  anything  was  known  as  to  the  normal  char- 
acter of  Littrow's  power  of  distinguishing  colors. 
His  answer  was  prompt  and  decisive.  "Oh  yes, 
Littrow  was  color-blind  to  red.  He  could  not  dis- 
tinguish between  the  color  of  Aldebaran  and  the 
whitest  star."  No  further  research  was  necessary. 
For  half  a  century  the  astronomical  world  had  based 
an  impression  on  the  innocent  but  mistaken  evidence 
of  a  color-blind  man — respecting  the  tints  of  ink  in  a 
manuscript. 

It  has  doubtless  happened  more  than  once  that 
when  an  intimate  friend  has  suddenly  and  unex- 
pectedly passed  away,  the  reader  has  ardently  wished 
that  it  were  possible  to  whisper  just  one  word  of  ap- 
preciation across  the  dark  abyss.  And  so  it  is  that 
I  have  ever  since  felt  that  I  would  like  greatly  to  tell 
Father  Hell  the  story  of  my  work  at  Vienna  in  1883. 


XVI 

THE    EVOLUTION    OF    THE    SCIENTIFIC 
INVESTIGATOR* 

A3  we  look  at  the  assemblage  gathered  in  this 
hall,  comprising  so  many  names  of  widest  re- 
nown in  every  branch  of  learning — we  might  almost 
say  in  every  field  of  human  endeavor — the  first  in- 
quiry suggested  must  be  after  the  object  of  our  meet- 
ing. The  answer  is  that  our  purpose  corresponds  to 
the  eminence  of  the  assemblage.  We  aim  at  nothing 
less  than  a  survey  of  the  realm  of  knowledge,  as  com- 
prehensive as  is  permitted  by  the  limitations  of  time 
and  space.  The  organizers  of  our  congress  have 
honored  me  with  the  charge  of  presenting  such  pre- 
liminary view  of  its  field  as  may  make  clear  the  spirit 
of  our  undertaking. 

Certain  tendencies  characteristic  of  the  science  of 
our  day  clearly  suggest  the  direction  of  our  thoughts 
most  appropriate  to  the  occasion.  Among  the 
strongest  of  these  is  one  towards  laying  greater  stress 
on  questions  of  the  beginnings  of  things,  and  regard- 
ing a  knowledge  of  the  laws  of  development  of  any 
object  of  study  as  necessary  to  the  understanding  of 
its  present  form.  It  may  be  conceded  that  the  prin- 
ciple here  involved  is  as  applicable  in  the  broad  field 

*  Presidential  address  at  the  opening  of  the  International  Con- 
gress of  Arts  and  Science,  St.  Louis  Exposition,  September  21,  1904. 

236 


. 


THE    SCIENTIFIC    INVESTIGATOR 


fore  us  as  in  a  special  research  into  the  properties 
of  the  minutest  organism.  It  therefore  seems  meet 
that  we  should  begin  by  inquiring  what  agency  has 
brought  about  the  remarkable  development  of  science 
to  which  the  world  of  to-day  bears  witness.  This 
view  is  recognized  in  the  plan  of  our  proceedings  by 
providing  for  each  great  department  of  knowledge 
a  review  of  its  progress  during  the  century  that  has 
elapsed  since  the  great  event  commemorated  by  the 
scenes  outside  this  hall.  But  such  reviews  do  not 
make  up  that  general  survey  of  science  at  large  which 
is  necessary  to  the  development  of  our  theme,  and 
which  must  include  the  action  of  causes  that  had 
their  origin  long  before  our  time.  The  movement 
which  culminated  in  making  the  nineteenth  century 
ever  memorable  in  history  is  the  outcome  of  a  long 
series  of  causes,  acting  through  many  centuries,  which 
are  worthy  of  especial  attention  on  such  an  occasion 
as  this.  In  setting  them  forth  we  should  avoid  lay- 
ing stress  on  those  visible  manifestations  which,  strik- 
ing the  eye  of  every  beholder,  are  in  no  danger  of 
being  overlooked,  and  search  rather  for  those  agencies 
whose  activities  underlie  the  whole  visible  scene, 
but  which  are  liable  to  be  blotted  out  of  sight  by  the 
very  brilliancy  of  the  results  to  which  they  have 
given  rise.  It  is  easy  to  draw  attention  to  the  won- 
derful qualities  of  the  oak ;  but,  from  that  very  fact, 
it  may  be  needful  to  point  out  that  the  real  wonder 
lies  concealed  in  the  acorn  from  which  it  grew. 

Our  inquiry  into  the  logical  order  of  the  causes 
which  have  made  our  civilization  what  it  is  to-day 
will  be  facilitated  by  bringing  to  mind  certain  ele- 
mentary considerations — ideas  so  familiar  that  set- 
ting them  forth  may  seem  like  citing  a  body  of 

237 


SIDE-LIGHTS    ON    ASTRONOMY 

truisms — and  yet  so  frequently  overlooked,  not  only 
individually,  but  in  their  relation  to  each  other,  that 
the  conclusion  to  which  they  lead  may  be  lost  to 
sight.  One  of  these  propositions  is  that  psychical 
rather  than  material  causes  are  those  which  we  should 
regard  as  fundamental  in  directing  the  development 
of  the  social  organism.  The  human  intellect  is  the 
really  active  agent  in  every  branch  of  endeavor— 
the  primum  mobile  of  civilization  —  and  all  those 
material  manifestations  to  which  our  attention  is 
so  often  directed  are  to  be  regarded  as  secondary  to 
this  first  agency.  If  it  be  true  that  "in  the  world  is 
nothing  great  but  man;  in  man  is  nothing  great  but 
mind,"  then  should  the  key-note  of  our  discourse  be 
the  recognition  of  this  first  and  greatest  of  powers. 

Another  well-known  fact  is  that  those  applications 
of  the  forces  of  nature  to  the  promotion  of  human 
welfare  which  have  made  our  age  what  it  is  are  of 
such  comparatively  recent  origin  that  we  need  go 
back  only  a  single  century  to  antedate  their  most 
important  features,  and  scarcely  more  than  four 
centuries  to  find  their  beginning.  It  follows  that  the 
subject  of  our  inquiry  should  be  the  commencement, 
not  many  centuries  ago,  of  a  certain  new  form  of  in- 
tellectual activity. 

Having  gained  this  point  of  view,  our  next  inquiry 
will  be  into  the  nature  of  that  activity  and  its  relation 
to  the  stages  of  progress  which  preceded  and  fol- 
lowed its  beginning.  The  superficial  observer,  who 
sees  the  oak  but  forgets  the  acorn,  might  tell  us  that 
the  special  qualities  which  have  brought  out  such 
great  results  are  expert  scientific  knowledge  and  rare 
ingenuity,  directed  to  the  application  of  the  powers 
of  steam  and  electricity.  From  this  point  of  view  the 

238 


THE    SCIENTIFIC    INVESTIGATOR 

great  inventors  and  the  great  captains  of  industry 
were  the  first  agents  in  bringing  about  the  modern 
era.  But  the  more  careful  inquirer  will  see  that  the 
work  of  these  men  was  possible  only  through  a  knowl- 
edge of  the  laws  of  nature,  which  had  been  gained  by 
men  whose  work  took  precedence  of  theirs  in  logical 
order,  and  that  success  in  invention  has  been  meas- 
ured by  completeness  in  such  knowledge.  While 
giving  all  due  honor  to  the  great  inventors,  let  us  re- 
member that  the  first  place  is  that  of  the  great  in- 
vestigators, whose  forceful  intellects  opened  the  way 
to  secrets  previously  hidden  from  men.  Let  it  be 
an  honor  and  not  a  reproach  to  these  men  that  they 
were  not  actuated  by  the  love  of  gain,  and  did  not 
keep  utilitarian  ends  in  view  in  the  pursuit  of  their 
researches.  If  it  seems  that  in  neglecting  such  ends 
they  were  leaving  undone  the  most  important  part 
of  their  work,  let  us  remember  that  Nature  turns  a 
forbidding  face  to  those  who  pay  her  court  with  the 
hope  of  gain,  and  is  responsive  only  to  those  suitors 
whose  love  for  her  is  pure  and  undefiled.  Not  only 
is  the  special  genius  required  in  the  investigator  not 
that  generally  best  adapted  to  applying  the  dis- 
coveries which  he  makes,  but  the  result  of  his  having 
sordid  ends  in  view  would  be  to  narrow  the  field  of 
his  efforts,  and  exercise  a  depressing  effect  upon  his 
activities.  The  true  man  of  science  has  no  such  ex- 
pression in  his  vocabulary  as  "useful  knowledge." 
His  domain  is  as  wide  as  nature  itself,  and  he  best 
fulfils  his  mission  when  he  leaves  to  others  the  task 
of  applying  the  knowledge  he  gives  to  the  world. 

We  have  here  the  explanation  of  the  well-known 
fact  that  the  functions  of  the  investigator  of  the  laws 
of  nature,  and  of  the  inventor  who  applies  these  laws 

239 


SIDE-LIGHTS    ON    ASTRONOMY 

to  utilitarian  purposes,  are  rarely  united  in  the  same 
person.  If  the  one  conspicuous  exception  which  the 
past  century  presents  to  this  rule  is  not  unique,  we 
should  probably  have  to  go  back  to  Watt  to  find 
another. 

From  this  view-point  it  is  clear  that  the  primary 
agent  in  the  movement  which  has  elevated  man  to 
the  masterful  position  he  now  occupies  is  the  scientific 
investigator.  He  it  is  whose  work  has  deprived 
plague  and  pestilence  of  their  terrors,  alleviated  hu- 
man suffering,  girdled  the  earth  with  the  electric  wire, 
bound  the  continent  with  the  iron  way,  and  made 
neighbors  of  the  most  distant  nations.  As  the  first 
agent  which  has  made  possible  this  meeting  of  his 
representatives,  let  his  evolution  be  this  day  our 
worthy  theme.  As  we  follow  the  evolution  of  an 
organism  by  studying  the  stages  of  its  growth,  so  we 
have  to  show  how  the  work  of  the  scientific  investi- 
gator is  related  to  the  ineffectual  efforts  of  his  prede- 
cessors. 

In  our  time  we  think  of  the  process  of  develop- 
ment in  nature  as  one  going  continuously  forward 
through  the  combination  of  the  opposite  processes 
of  evolution  and  dissolution.  The  tendency  of  our 
thought  has  been  in  the  direction  of  banishing  cata- 
clysms to  the  theological  limbo,  and  viewing  Nature 
as  a  sleepless  plodder,  endowed  with  infinite  patience, 
waiting  through  long  ages  for  results.  I  do  not  con- 
test the  truth  of  the  principle  of  continuity  on  which 
this  view  is  based.  But  it  fails  to  make  known  to 
us  the  whole  truth.  The  building  of  a  ship  from  the 
time  that  her  keel  is  laid  until  she  is  making  her  way 
across  the  ocean  is  a  slow  and  gradual  process;  yet 
there  is  a  cataclysmic  epoch  opening  up  a  new  era  in 

240 


THE    SCIENTIFIC    INVESTIGATOR 

her  history.  It  is  the  moment  when,  after  lying  for 
months  or  years  a  dead,  inert,  immovable  mass,  she  is 
suddenly  endowed  with  the  power  of  motion,  and,  as 
if  imbued  with  life,  glides  into  the  stream,  eager  to 
begin  the  career  for  which  she  was  designed. 

I  think  it  is  thus  in  the  development  of  humanity. 
Long  ages  may  pass  during  which  a  race,  to  all  ex- 
ternal observation,  appears  to  be  making  no  real 
progress.  Additions  may  be  made  to  learning,  and 
the  records  of  history  may  constantly  grow,  but  there 
is  nothing  in  its  sphere  of  thought,  or  in  the  features 
of  its  life,  that  can  be  called  essentially  new.  Yet, 
Nature  may  have  been  all  along  slowly  working  in  a 
way  which  evades  our  scrutiny,  until  the  result  of 
her  operations  suddenly  appears  in  a  new  and  revolu- 
tionary movement,  carrying  the  race  to-  a  higher 
plane  of  civilization. 

It  is  not  difficult  to  point  out  such  epochs  in  hu- 
man progress.  The  greatest  of  all,  because  it  was  the 
first,  is  one  of  which  we  find  no  record  either  in 
written  or  geological  history.  It  was  the  epoch  when 
our  progenitors  first  took  conscious  thought  of  the 
morrow,  first  used  the  crude  weapons  which  Nature 
had  placed  within  their  reach  to  kill  their  prey,  first 
built  a  fire  to  warm  their  bodies  and  cook  their  food. 
I  love  to  fancy  that  there  was  some  one  first  man, 
the  Adam  of  evolution,  who  did  all  this,  and  who 
used  the  power  thus  acquired  to  show  his  fellows 
how  they  might  profit  by  his  example.  When  the 
members  of  the  tribe  or  community  which  he  gath- 
ered around  him  began  to  conceive  of  life  as  a  whole 
—to  include  yesterday,  to-day,  and  to-morrow  in 
the  same  mental  grasp  —  to  think  how  they  might 
apply  the  gifts  of  Nature  to  their  own  uses — a  move- 

241 


SIDE-LIGHTS    ON    ASTRONOMY 

ment  was  begun  which  should  ultimately  lead  to  civ-! 
ilization. 

Long  indeed  must  have  been  the  ages  required  for 
the  development  of  this  rudest  primitive  community 
into  the  civilization  revealed  to  us  by  the  most  an- 
cient tablets  of  Egypt  and  Assyria.  After  spoken 
language  was  developed,  and  after  the  rude  represen- 
tation of  ideas  by  visible  marks  drawn  to  resemble 
them  had  long  been  practised,  some  Cadmus  must 
have  invented  an  alphabet.  When  the  use  of  written 
language  was  thus  introduced,  the  word  of  command 
ceased  to  be  confined  to  the  range  of  the  human 
voice,  and  it  became  possible  for  master  minds  to 
extend  their  influence  as  far  as  a  written  message 
could  be  carried.  Then  were  communities  gathered 
into  provinces;  provinces  into  kingdoms;  kingdoms 
into  great  empires  of  antiquity.  Then  arose  a  stage 
of  civilization  which  we  find  pictured  in  the  most 
ancient  records — a  stage  in  which  men  were  governed 
by  laws  that  were  perhaps  as  wisely  adapted  to  their 
conditions  as  our  laws  are  to  ours — in  which  the 
phenomena  of  nature  were  rudely  observed,  and 
striking  occurrences  in  the  earth  or  in  the  heavens 
recorded  in  the  annals  of  the  nation. 

Vast  was  the  progress  of  knowledge  during  the  in- 
terval between  these  empires  and  the  century  in 
which  modern  science  began.  Yet,  if  I  am  right  in 
making  a  distinction  between  the  slow  and  regular 
steps  of  progress,  each  growing  naturally  out  of  that 
which  preceded  it,  and  the  entrance  of  the  mind  at 
some  fairly  definite  epoch  into  an  entirely  new  sphere 
of  activity,  it  would  appear  that  there  was  only  one 
such  epoch  during  the  entire  interval.  This  was  when 
abstract  geometrical  reasoning  commenced,  and  as- 

242 


THE    SCIENTIFIC    INVESTIGATOR 

tronomical  observations  aiming  at  precision  were  re- 
corded, compared,  and  discussed.  Closely  associated 
with  it  must  have  been  the  construction  of  the  forms 
of  logic.  The  radical  difference  between  the  demon- 
stration of  a  theorem  of  geometry  and  the  reasoning 
of  every-day  life  which  the  masses  of  men  must  have 
practised  from  the  beginning,  and  which  few  even 
to-day  ever  get  beyond,  is  so  evident  at  a  glance  that 
I  need  not  dwell  upon  it.  The  principal  feature  of 
this  advance  is  that,  by  one  of  those  antinomies  of 
human  intellect  of  which  examples  are  not  wanting 
even  in  our  own  time,  the  development  of  abstract 
ideas  preceded  the  concrete  knowledge  of  natural 
phenomena.  When  we  reflect  that  in  the  geometry 
of  Euclid  the  science  of  space  was  brought  to  such 
logical  perfection  that  even  to-day  its  teachers  are 
not  agreed  as  to  the  practicability  of  any  great  im- 
provement upon  it,  we  cannot  avoid  the  feeling  that 
a  very  slight  change  in  the  direction  of  the  intel- 
lectual activity  of  the  Greeks  would  have  led  to  the 
beginning  of  natural  science.  But  it  would  seem  that 
the  very  purity  and  perfection  which  was  aimed  at  in 
their  system  of  geometry  stood  in  the  way  of  any 
extension  or  application  of  its  methods  and  spirit  to 
the  field  of  nature.  One  example  of  this  is  worthy 
of  attention.  In  modern  teaching  the  idea  of  magni- 
tude as  generated  by  motion  is  freely  introduced.  A 
line  is  described  by  a  moving  point;  a  plane  by  a 
moving  line ;  a  solid  by  a  moving  plane.  It  may,  at 
first  sight,  seem  singular  that  this  conception  finds 
no  place  in  the  Euclidian  system.  But  we  may  re- 
gard the  omission  as  a  mark  of  logical  purity  and 
rigor.  Had  the  real  or  supposed  advantages  of  in- 
troducing motion  into  geometrical  conceptions  been 

243 


SIDE-LIGHTS    ON    ASTRONOMY 

suggested  to  Euclid,  we  may  suppose  him  to  have 
replied  that  the  theorems  of  space  are  independent 
of  time;  that  the  idea  of  motion  necessarily  implies 
time,  and  that,  in  consequence,  to  avail  ourselves  of 
it  would  be  to  introduce  an  extraneous  element  into 
geometry. 

It  is  quite  possible  that  the  contempt  of  the  ancient 
philosophers  for  the  practical  application  of  their 
science,  which  has  continued  in  some  form  to  our 
own  time,  and  which  is  not  altogether  unwholesome, 
was  a  powerful  factor  in  the  same  direction.  The 
result  was  that,  in  keeping  geometry  pure  from  ideas 
which  did  not  belong  to  it,  it  failed  to  form  what  might 
otherwise  have  been  the  basis  of  physical  science. 
Its  founders  missed  the  discovery  that  methods  simi- 
lar to  those  of  geometric  demonstration  could  be 
extended  into  other  and  wider  fields  than  that  of 
space.  Thus  not  only  the  development  of  applied 
geometry  but  the  reduction  of  other  conceptions  to 
a  rigorous  mathematical  form  was  indefinitely  post- 
poned. 

There  is,  however,  one  science  which  admitted  of 
the  immediate  application  of  the  theorems  of  geome- 
try, and  which  did  not  require  the  application  of  the 
experimental  method.  Astronomy  is  necessarily  a 
science  of  observation  pure  and  simple,  in  which  ex- 
periment can  have  no  place  except  as  an  auxiliary. 
The  vague  accounts  of  striking  celestial  phenomena 
handed  down  by  the  priests  and  astrologers  of  an- 
tiquity were  followed  in  the  time  of  the  Greeks  by 
observations  having,  in  form  at  least,  a  rude  approach 
to  precision,  though  nothing  like  the  degree  of  preci- 
sion that  the  astronomer  of  to-day  would  reach  with 
the  naked  eye,  aided  by  such  instruments  as  he  could 

244 


THE    SCIENTIFIC    INVESTIGATOR 

fashion  from  the  tools  at  the  command  of  the 
ancients. 

The  rude  observations  commenced  by  the  Baby- 
lonians were  continued  with  gradually  improving  in- 
struments— first  by  the  Greeks  and  afterwards  by  the 
Arabs — but  the  results  failed  to  afford  any  insight  into 
the  true  relation  of  the  earth  to  the  heavens.  What 
was  most  remarkable  in  this  failure  is  that,  to  take 
a  first  step  forward  which  would  have  led  on  to  suc- 
cess, no  more  was  necessary  than  a  course  of  abstract 
thinking  vastly  easier  than  that  required  for  working 
out  the  problems  of  geometry.  That  space  is  infinite 
is  an  unexpressed  axiom,  tacitly  assumed  by  Euclid 
and  his  successors.  Combining  this  with  the  most 
elementary  consideration  of  the  properties  of  the  tri- 
angle, it  would  be  seen  that  a  body  of  any  given  size 
could  be  placed  at  such  a  distance  in  space  as  to  ap- 
pear to  us  like  a  point.  Hence  a  body  as  large  as  our 
earth,  which  was  known  to  be  a  globe  from  the  time 
that  the  ancient  Phoenicians  navigated  the  Mediter- 
ranean, if  placed  in  the  heavens  at  a  sufficient  dis- 
tance, would  look  like  a  star.  The  obvious  conclu- 
sion that  the  stars  might  be  bodies  like  our  globe, 
shining  either  by  their  own  light  or  by  that  of  the 
sun,  would  have  been  a  first  step  to  the  understanding 
of  the  true  system  of  the  world. 

There  is  historic  evidence  that  this  deduction  did 
not  wholly  escape  the  Greek  thinkers.  It  is  true 
that  the  critical  student  will  assign  little  weight  to 
the  current  belief  that  the  vague  theory  of  Pythagoras 
— that  fire  was  at  the  centre  of  all  things — implies  a 
conception  of  the  heliocentric  theory  of  the  solar 
system.  But  the  testimony  of  Archimedes,  con- 
fused though  it  is  in  form,  leaves  no  serious  doubt 


SIDE-LIGHTS    ON    ASTRONOMY 

that  Aristarchus  of  Samos  not  only  propounded  the 
view  that  the  earth  revolves  both  on  its  own  axis 
and  around  the  sun,  but  that  he  correctly  removed 
the  great  stumbling-block  in  the  way  of  this  theory 
by  adding  that  the  distance  of  the  fixed  stars  was 
infinitely  greater  than  the  dimensions  of  the  earth's 
orbit.  Even  the  world  of  philosophy  was  not  yet 
ready  for  this  conception,  and,  so  far  from  seeing  the 
reasonableness  of  the  explanation,  we  find  Ptolemy 
arguing  against  the  rotation  of  the  earth  on  grounds 
which  careful  observations  of  the  phenomena  around 
him  would  have  shown  to  be  ill-founded. 

Physical  science,  if  we  can  apply  that  term  to  an 
unco-ordinated  body  of  facts,  was  successfully  culti- 
vated from  the  earliest  times.  Something  must  have 
been  known  of  the  properties  of  metals,  and  the  art 
of  extracting  them  from  their  ores  must  have  been 
practised,  from  the  time  that  coins  and  medals  were 
first  stamped.  The  properties  of  the  most  common 
compounds  were  discovered  by  alchemists  in  their 
vain  search  for  the  philosopher's  stone,  but  no  actual 
progress  worthy  of  the  name  rewarded  the  practi- 
tioners of  the  black  art. 

Perhaps  the  first  approach  to  a  correct  method  was 
that  of  Archimedes,  who  by  much  thinking  worked 
out  the  law  of  the  lever,  reached  the  conception  of  the 
centre  of  gravity,  and  demonstrated  the  first  prin- 
ciples of  hydrostatics.  It  is  remarkable  that  he  did 
not  extend  his  researches  into  the  phenomena  of 
motion,  whether  spontaneous  or  produced  by  force. 
The  stationary  condition  of  the  human  intellect  is 
most  strikingly  illustrated  by  the  fact  that  not  until 
the  time  of  Leonardo  was  any  substantial  advance 
made  on  his  discovery.  To  sum  up  in  one  sentence 

246 


THE    SCIENTIFIC    INVESTIGATOR 


the  most  characteristic  feature  of  ancient  and  medie- 
val science,  we  see  a  notable  contrast  between  the 
precision  of  thought  implied  in  the  construction  and 
demonstration  of  geometrical  theorems  and  the 
vague  indefinite  character  of  the  ideas  of  natural 
phenomena  generally,  a  contrast  which  did  not  dis- 
appear until  the  foundations  of  modern  science  began 
to  be  laid. 

We  should  miss  the  most  essential  point  of  the 
difference  between  medieval  and  modern  learning  if 
we  looked  upon  it  as  mainly  a  difference  either  in  the 
precision  or  the  amount  of  knowledge.  The  develop- 
ment of  both  of  these  qualities  would,  under  any  cir- 
cumstances, have  been  slow  and  gradual,  but  sure. 
We  can  hardly  suppose  that  any  one  generation,  or 
even  any  one  century,  would  have  seen  the  complete 
substitution  of  exact  for  inexact  ideas.  Slowness  of 
growth  is  as  inevitable  in  the  case  of  knowledge  as  in 
that  of  a  growing  organism.  The  most  essential 
point  of  difference  is  one  of  those  seemingly  slight 
ones,  the  importance  of  which  we  are  too  apt  to  over- 
look. It  was  like  the  drop  of  blood  in  the  wrong 
place,  which  some  one  has  told  us  makes  all  the  dif- 
ference between  a  philosopher  and  a  maniac.  It  was 
all  the  difference  between  a  living  tree  and  a  dead 
one,  between  an  inert  mass  and  a  growing  organism. 
The  transition  of  knowledge  from  the  dead  to  the 
living  form  must,  in  any  complete  review  of  the  sub- 
ject, be  looked  upon  as  the  really  great  event  of  mod- 
ern times.  Before  this  event  the  intellect  was  bound 
down  by  a  scholasticism  which  regarded  knowledge 
as  a  rounded  whole,  the  parts  of  which  were  written 
in  books  and  carried  in  the  minds  of  learned  men. 
The  student  was  taught  from  the  beginning  of  his 
17  247 


SIDE-LIGHTS    ON    ASTRONOMY 

work  to  look  upon  authority  as  the  foundation  of 
his  beliefs.  The  older  the  authority  the  greater  the 
weight  it  carried.  So  effective  was  this  teaching 
that  it  seems  never  to  have  occurred  to  individual 
men  that  they  had  all  the  opportunities  ever  enjoyed 
by  Aristotle  of  discovering  truth,  with  the  added 
advantage  of  all  his  knowledge  to  begin  with.  Ad- 
vanced as  was  the  development  of  formal  logic,  that 
practical  logic  was  wanting  which  could  see  that  the 
last  of  a  series  of  authorities,  every  one  of  which 
rested  on  those  which  preceded  it,  could  never  form 
a  surer  foundation  for  any  doctrine  than  that  sup- 
plied by  its  original  propounder. 

The  result  of  this  view  of  knowledge  was  that,  al- 
though during  the  fifteen  centuries  following  the 
death  of  the  geometer  of  Syracuse  great  universities 
were  founded  at  which  generations  of  professors  ex- 
pounded all  the  learning  of  their  time,  neither  pro- 
fessor nor  student  ever  suspected  what  latent  possi- 
bilities of  good  were  concealed  in  the  most  familiar 
operations  of  Nature.  Every  one  felt  the  wind  blow, 
saw  water  boil,  and  heard  the  thunder  crash,  but 
never  thought  of  investigating  the  forces  here  at 
play.  Up  to  the  middle  of  the  fifteenth  century  the 
most  acute  observer  could  scarcely  have  seen  the 
dawn  of  a  new  era. 

In  view  of  this  state  of  things  it  must  be  regarded 
as  one  of  the  most  remarkable  facts  in  evolutionary 
history  that  four  or  five  men,  whose  mental  constitu- ] 
tion  was  either  typical  of  the  new  order  of  things,  or 
who  were  powerful  agents  in  bringing  it  about,  were 
all  born  during  the  fifteenth  century,  four  of  them  at 
least,  at  so  nearly  the  same  time  as  to  be  contempo- 
raries. 

248 


THE    SCIENTIFIC    INVESTIGATOR 

Leonardo  da  Vinci,  whose  artistic  genius  has  charm- 
ed succeeding  generations,  was  also  the  first  practi- 
cal engineer  of  his  time,  and  the  first  man  after 
Archimedes  to  make  a  substantial  advance  in  develop- 
ing the  laws  of  motion.  That  the  world  was  not  pre- 
pared to  make  use  of  his  scientific  discoveries  does 
not  detract  from  the  significance  which  must  attach 
to  the  period  of  his  birth. 

Shortly  after  him  was  born  the  great  navigator 
whose  bold  spirit  was  to  make  known  a  new  world, 
thus  giving  to  commercial  enterprise  that  impetus 
which  was  so  powerful  an  agent  in  bringing  about  a 
revolution  in  the  thoughts  of  men. 

The  birth  of  Columbus  was  soon  followed  by  that 
of  Copernicus,  the  first  after  Aristarchus  to  demon- 
strate the  true  system  of  the  world.     In  him  more 
than  in  any  of  his  contemporaries  do  we   see   the 
struggle  between  the  old  forms  of  thought  and  the 
new.     It  seems  almost  pathetic  and  is  certainly  most 
i  suggestive  of  the  general  view  of  knowledge  taken  at 
';  that  time  that,  instead  of  claiming  credit  for  bring- 
|  ing  to  light  great  truths  before  unknown,  he  made  a 
j  labored  attempt  to  show  that,  after  all,  there  was 
j  nothing  really  new  in  his  system,  which  he  claimed 
to  date  from  Pythagoras  and  Philolaus.     In  this  con- 
I  nee t  ion  it  is  curious  that  he  makes  no  mention  of 
i  Aristarchus,  who  I  think  will  be  regarded  by  conserv- 
ative historians  as  his  only  demonstrated  predecessor, 
j  To  the  hold  of  the  older  ideas  upon  his  mind  we  must 
,  attribute  the  fact  that  in  constructing  his  system  he 
j  took  great  pains  to  make  as  little  change  as  possible 
in  ancient  conceptions. 

Luther,  the  greatest  thought-stirrer  of  them  all, 
practically  of  the  same  generation  with  Copernicus, 

249 


SIDE-LIGHTS    ON    ASTRONOMY 

Leonardo  and  Columbus,  does  not  come  in  as  a  scien- 
tific investigator,  but  as  the  great  loosener  of  chains 
which  had  so  fettered  the  intellect  of  men  that  they 
dared  not  think  otherwise  than  as  the  authorities 
thought. 

Almost  coeval  with  the  advent  of  these  intellects 
was  the  invention  of  printing  with  movable  type. 
Gutenberg  was  born  during  the  first  decade  of  the 
century,  and  his  associates  and  others  credited  with 
the  invention  not  many  years  afterwards.  If  we 
accept  the  principle  on  which  I  am  basing  my  argu- 
ment, that  in  bringing  out  the  springs  of  our  prog- 
ress we  should  assign  the  first  place  to  the  birth 
of  those  psychic  agencies  which  started  men  on  new 
lines  of  thought,  then  surely  was  the  fifteenth  the 
wonderful  century. 

Let  us  not  forget  that,  in  assigning  the  actors  then 
born  to  their  places,  we  are  not  narrating  history, 
but  studying  a  special  phase  of  evolution.  It  mat- 
ters not  for  us  that  no  university  invited  Leonardo 
to  its  halls,  and  that,  his  science  was  valued  by  his 
contemporaries  only  as  an  adjunct  to  the  art  of  en- 
gineering. The  great  fact  still  is  that  he  was  the 
first  of  mankind  to  propound  laws  of  motion.  It  is 
not  for  anything  in  Luther 's  doctrines  that  he  finds 
a  place  in  our  scheme.  No  matter  for  us  whether 
they  were  sound  or  not.  What  he  did  towards  the 
evolution  of  the  scientific  investigator  was  to  show 
by  his  example  that  a  man  might  question  the  best- 
established  and  most  venerable  authority  and  still 
live  —  still  preserve  his  intellectual  integrity  —  still 
command  a  hearing  from  nations  and  their  rulers. 
It  matters  not  for  us  whether  Columbus  ever  knew 
that  he  had  discovered  a  new  continent.  His  work 

250 


THE    SCIENTIFIC    INVESTIGATOR 

was  to  teach  that  neither  hydra,  chimera  nor  abyss 
— neither  divine  injunction  nor  infernal  machination 
— was  in  the  way  of  men  visiting  every  part  of  the 
globe,  and  that  the  problem  of  conquering  the  world 
reduced  itself  to  one  of  sails  and  rigging,  hull  and 
compass.  The  better  part  of  Copernicus  was  to  di- 
rect man  to  a  view-point  whence  he  should  see  that 
the  heavens  were  of  like  matter  with  the  earth.  All 
this  done,  the  acorn  was  planted  from  which  the  oak 
of  our  civilization  should  spring.  The  mad  quest  for 
gold  which  followed  the  discovery  of  Columbus,  the 
questionings  which  absorbed  the  attention  of  the 
learned,  the  indignation  excited  by  the  seeming 
vagaries  of  a  Paracelsus,  the  fear  and  trembling  lest 
the  strange  doctrine  of  Copernicus  should  undermine 
the  faith  of  centuries,  were  all  helps  to  the  germina- 
tion of  the  seed — stimuli  to  thought  which  urged  it 
on  to  explore  the  new  fields  opened  up  to  its  occupa- 
tion. This  given,  all  that  has  since  followed  came 
out  in  regular  order  of  development,  and  need  be 
here  considered  only  in  those  phases  having  a  special 
relation  to  the  purpose  of  our  present  meeting. 

So  slow  was  the  growth  at  first  that  the  sixteenth 
century  may  scarcely  have  recognized  the  inaugura- 
tion of  a  new  era.  Torricelli  and  Benedetti  were  of 
the  third  generation  after  Leonardo,  and  Galileo,  the 
first  to  make  a  substantial  advance  upon  his  theory, 
was  born  more  than  a  century  after  him.  Only  two 
or  three  men  appeared  in  a  generation  who,  working 
alone,  could  make  real  progress  in  discovery,  and 
even  these  could  do  little  in  leavening  the  minds  of 
their  fellowmen  with  the  new  ideas. 

Up  to  the  middle  of  the  seventeenth  century  an 
agent  which  all  experience  since  that  time  shows  to 

251 


SIDE-.LIGHTS    ON    ASTRONOMY 

be  necessary  to  the  most  productive  intellectual  ac- 
tivity was  wanting.  This  was  the  attrition  of  like 
minds,  making  suggestions  to  one  another,  criticising, 
comparing,  and  reasoning.  This  element  was  intro- 
duced by  the  organization  of  the  Royal  Society  of 
London  and  the  Academy  of  Sciences  of  Paris. 

The  members  of  these  two  bodies  seem  like  in- 
genious youth  suddenly  thrown  into  a  new  world  of 
interesting  objects,  the  purposes  and  relations  of 
which  they  had  to  discover.  The  novelty  of  the  sit- 
uation is  strikingly  shown  in  the  questions  which 
occupied  the  minds  of  the  incipient  investigators. 
One  natural  result  of  British  maritime  enterprise  was 
that  the  aspirations  of  the  Fellows  of  the  Royal  So- 
ciety were  not  confined  to  any  continent  or  hemi- 
sphere. Inquiries  were  sent  all  the  way  to  Batavia 
to  know  "  whether  there  be  a  hill  in  Sumatra  which 
burneth  continually,  and  a  fountain  which  runneth 
pure  balsam."  The  astronomical  precision  with 
which  it  seemed  possible  that  physiological  opera- 
tions might  go  on  was  evinced  by  the  inquiry  whether 
the  Indians  can  so  prepare  that  stupefying  herb 
Datura  that  "  they  make  it  lie  several  days,  months, 
years,  according  as  they  will,  in  a  man's  body  with- 
out doing  him  any  harm,  and  at  the  end  kill  him 
without  missing  an  hour's  time."-  Of  this  continent 
one  of  the  inquiries  was  whether  there  be  a  tree  in 
Mexico  that  yields  water,  wine,  vinegar,  milk,  honey, 
wax,  thread  and  needles. 

Among  the  problems  before  the  Paris  Academy  of 
Sciences  those  of  physiology  and  biology  took  a 
prominent  place.  The  distillation  of  compounds  had 
long  been  practised,  and  the  fact  that  the  more 
spirituous  elements  of  certain  substances  were  thus 

252 


THE    SCIENTIFIC    INVESTIGATOR 

separated  naturally  led  to  the  question  whether  the 
essential  essences  of  life  might  not  be  discoverable 
in  the  same  way.  In  order  that  all  might  partici- 
pate in  the  experiments,  they  were  conducted  in 
open  session  of  the  academy,  thus  guarding  against 
the  danger  of  any  one  member  obtaining  for  his  ex- 
clusive personal  use  a  possible  elixir  of  life.  A  wide 
range  of  the  animal  and  vegetable  kingdom,  including 
cats,  dogs  and  birds  of  various  species,  were  thus 
analyzed.  The  practice  of  dissection  was  intro- 
duced on  a  large  scale.  That  of  the  cadaver  of  an 
elephant  occupied  several  sessions,  and  was  of  such 
interest  that  the  monarch  himself  was  a  spectator. 

To  the  same  epoch  with  the  formation  and  first 
work  of  these  two  bodies  belongs  the  invention  of  a 
mathematical  method  which  in  its  importance  to  the 
advance  of  exact  science  may  be  classed  with  the 
invention  of  the  alphabet  in  its  relation  to  the  prog- 
ress of  society  at  large.  The  use  of  algebraic  sym- 
bols to  represent  quantities  had  its  origin  before  the 
commencement  of  the  new  era,  and  gradually  grew 
into  a  highly  developed  form  during  the  first  two 
centuries  of  that  era.  But  this  method  could  repre- 
sent quantities  only  as  fixed.  It  is  true  that  the 
elasticity  inherent  in  the  use  of  such  symbols  per- 
mitted of  their  being  applied  to  any  and  every 
quantity;  yet,  in  any  one  application,  the  quantity 
was  considered  as  fixed  and  definite.  But  most  of 
the  magnitudes  of  nature  are  in  a  state  of  continual 
variation;  indeed,  since  all  motion  is  variation,  the 
latter  is  a  universal  characteristic  of  all  phenomena. 
No  serious  advance  could  be  made  in  the  application 
of  algebraic  language  to  the  expression  of  physical 
phenomena  until  it  could  be  so  extended  as  to  ex- 

253 


SIDE-LIGHTS    ON    ASTRONOMY 

press  variation  in  quantities,  as  well  as  the  quantities 
themselves.  This  extension,  worked  out  indepen- 
dently by  Newton  and  Leibnitz,  may  be  classed  as 
the  most  fruitful  of  conceptions  in  exact  science. 
With  it  the  way  was  opened  for  the  unimpeded  and 
continually  accelerated  progress  of  the  last  two 
centuries. 

The  feature  of  this  period  which  has  the  closest 
relation  to  the  purpose  of  our  coming  together  is  the 
seemingly  unending  subdivision  of  knowledge  into 
specialties,  many  of  which  are  becoming  so  minute 
and  so  isolated  that  they  seem  to  have  no  interest  for 
any  but  their  few  pursuers.  Happily  science  itself 
has  afforded  a  corrective  for  its  own  tendency  in  this 
direction.  The  careful  thinker  will  see  that  in  these 
seemingly  diverging  branches  common  elements  and 
common  principles  are  coming  more  and  more  to 
light.  There  is  an  increasing  recognition  of  methods 
of  research,  and  of  deduction,  which  are  common  to 
large  branches,  or  to  the  whole  of  science.  We  are 
more  and  more  recognizing  the  principle  that  prog- 
ress in  knowledge  implies  its  reduction  to  more  exact 
forms,  and  the  expression  of  its  ideas  in  language 
more  or  less  mathematical.  The  problem  before  the 
organizers  of  this  Congress  was,  therefore,  to  bring 
the  sciences  together,  and  seek  for  the  unity  which 
we  believe  underlies  their  infinite  diversity. 

The  assembling  of  such  a  body  as  now  fills  this 
hall  was  scarcely  possible  in  any  preceding  genera- 
tion, and  is  made  possible  now  only  through  the 
agency  of  science  itself.  It  differs  from  all  preced- 
ing international  meetings  by  the  universality  of  its 
scope,  which  aims  to  include  the  whole  of  knowledge. 
It  is  also  unique  in  that  none  but  leaders  have  been 

254 


THE    SCIENTIFIC    INVESTIGATOR 

sought  out  as  members.  It  is  unique  in  that  so 
many  lands  have  delegated  their  choicest  intellects 
to  carry  on  its  work.  They  come  from  the  country 
to  which  our  republic  is  indebted  for  a  third  of  its 
territory,  including  the  ground  on  which  we  stand; 
from  the  land  which  has  taught  us  that  the  most 
scholarly  devotion  to  the  languages  and  learning  of 
the  cloistered  past  is  compatible  with  leadership  in 
the  practical  application  of  modern  science  to  the 
arts  of  life ;  from  the  island  whose  language  and  litera- 
ture have  found  a  new  field  and  a  vigorous  growth  in 
this  region;  from  the  last  seat  of  the  holy  Roman 
Empire;  from  the  country  which,  remembering  a 
monarch  who  made  an  astronomical  observation  at 
the  Greenwich  Observatory,  has  enthroned  science 
in  one  of  the  highest  places  in  its  government;  from 
the  peninsula  so  learned  that  we  have  invited  one  of 
its  scholars  to  come  and  tells  us  of  our  own  language ; 
from  the  land  which  gave  birth  to  Leonardo,  Galileo, 
Torricelli,  Columbus,  Volta — what  an  array  of  im- 
mortal names! — from  the  little  republic  of  glorious 
history  which,  breeding  men  rugged  as  its  eternal 
snow-peaks,  has  yet  been  the  seat  of  scientific  in- 
vestigation since  the  day  of  the  Bernoullis ;  from  the 
land  whose  heroic  dwellers  did  not  hesitate  to  use 
the  ocean  itself  to  protect  it  against  invaders,  and 
which  now  makes  us  marvel  at  the  amount  of  erudi- 
tion compressed  within  its  little  area;  from  the 
nation  across  the  Pacific,  which,  by  half  a  century 
of  unequalled  progress  in  the  arts  of  life,  has  made 
an  important  contribution  to  evolutionary  science 
through  demonstrating  the  falsity  of  the  theory  that 
the  most  ancient  races  are  doomed  to  be  left  in  the 
rear  of  the  advancing  age — in  a  word,  from  every 

255 


SIDE-LIGHTS    ON    ASTRONOMY 

great  centre  of  intellectual  activity  on  the  globe  I 
see  before  me  eminent  representatives  of  that  world- 
advance  in  knowledge  which  we  have  met  to  cele- 
brate. May  we  not  confidently  hope  that  the  dis- 
cussions of  such  an  assemblage  will  prove  pregnant 
of  a  future  for  science  which  shall  outshine  even  its 
brilliant  past. 

Gentlemen  and  scholars  all!  You  do  not  visit  our 
shores  to  find  great  collections  in  which  centuries 
of  humanity  have  given  expression  on  canvas  and  in 
marble  to  their  hopes,  fears,  and  aspirations.  Nor  do 
you  expect  institutions  and  buildings  hoary  with  age. 
But  as  you  feel  the  vigor  latent  in  the  fresh  air  of 
these  expansive  prairies,  which  has  collected  the 
products  of  human  genius  by  which  we  are  here  sur- 
rounded, and,  I  may  add,  brought  us  together;  as 
you  study  the  institutions  which  we  have  founded  for 
the  benefit,  not  only  of  our  own  people,  but  of  hu- 
manity at  large;  as  you  meet  the  men  who,  in  the 
short  space  of  one  century,  have  transformed  this 
valley  from  a  savage  wilderness  into  what  it  is  to- 
day— then  may  you  find  compensation  for  the  want 
of  a  past  like  yours  by  seeing  with  prophetic  eye  a 
future  world-power  of  which  this  region  shall  be  the 
seat.  If  such  is  to  be  the  outcome  of  the  institutions 
which  we  are  now  building  up,  then  may  your  pres- 
ent visit  be  a  blessing  both  to  your  posterity  and 
ours  by  making  that  power  one  for  good  to  all  man- 
kind. Your  deliberations  will  help  to  demonstrate 
to  us  and  to  the  world  at  large  that  the  reign  of  law 
must  supplant  that  of  brute  force  in  the  relations  of 
the  nations,  just  as  it  has  supplanted  it  in  the  rela- 
tions of  individuals.  You  will  help  to  show  that  the 
war  which 'science  is  now  waging  against  the  sources 


THE    SCIENTIFIC    INVESTIGATOR 

of  diseases,  pain,  and  misery  offers  an  even  nobler 
field  for  the  exercise  of  heroic  qualities  than  can 
that  of  battle.  We  hope  that  when,  after  your  all 
too-fleeting  sojourn  in  our  midst,  you  return  to  your 
own  shores,  you  will  long  feel  the  influence  of  the  new 
air  you  have  breathed  in  an  infusion  of  increased 
vigor  in  pursuing  your  varied  labors.  And  if  a  new 
impetus  is  thus  given  to  the  great  intellectual  move- 
ment of  the  past  century,  resulting  not  only  in  pro- 
moting the  unification  of  knowledge,  but  in  widen- 
ing its  field  through  new  combinations  of  effort  on 
the  part  of  its  votaries,  the  projectors,  organizers  and 
supporters  of  this  Congress  of  Arts  and  Science  will 
be  justified  of  their  labors. 


XVII 

THE   EVOLUTION   OF   ASTRONOMICAL   KNOWL- 
EDGE* 
> 

ASSEMBLED,  as  we  are,  to  dedicate  a  new  in- 
f\  stitution  to  the  promotion  of  our  knowledge  of 
the  heavens,  it  appeared  to  me  that  an  appropriate 
and  interesting  subject  might  be  the  present  and 
future  problems  of  astronomy.  Yet  it  seemed,  on 
further  reflection,  that,  apart  from  the  difficulty  of 
making  an  adequate  statement  of  these  problems  on 
such  an  occasion  as  the  present,  such  a  wording  of 
the  theme  would  not  fully  express  the  idea  which  I 
wish  to  convey.  The  so-called  problems  of  astronomy 
are  not  separate  and  independent,  but  are  rather  the 
parts  of  one  great  problem,  that  of  increasing  our 
knowledge  of  the  universe  in  its  widest  extent.  Nor 
is  it  easy  to  contemplate  the  edifice  of  astronomical 
science  as  it  now  stands,  without  thinking  of  the 
past  as  well  as  of  the  present  and  future.  The  fact 
is  that  our  knowledge  of  the  universe  has  been  in  the 
nature  of  a  slow  and  gradual  evolution,  commencing 
at  a  very  early  period  in  human  history,  and  destined 
to  go  forward  without  stop,  as  we  hope,  so  long  as 
civilization  shall  endure.  The  astronomer  of  every 
age  has  built  on  the  foundations  laid  by  his  predeces- 
sors, and  his  work  has  always  formed,  and  must  ever 

*  Address  at  the  dedication  of  the  Flower  Observatory,  Univer- 
sity of  Pennsylvania,  May  12,  1897. — Science,  May  21,  1897. 

258 


ASTRONOMICAL    KNOWLEDGE 

form,  the  base  on  which  his  successors  shall  build. 
The  astronomer  of  to-day  may  look  back  upon  Hip- 
parchus  and  Ptolemy  as  the  earliest  ancestors  of 
whom  he  has  positive  knowledge.  He  can  trace  his 
scientific  descent  from  generation  to  generation, 
through  the  periods  of  Arabian  and  medieval  science, 
through  Copernicus,  Kepler,  Newton,  Laplace,  and 
Herschel,  down  to  the  present  time.  The  evolution 
of  astronomical  knowledge,  generally  slow  and  grad- 
ual, offering  little  to  excite  the  attention  of  the  pub- 
lic, has  yet  been  marked  by  two  cataclysms.  One 
of  these  is  seen  in  the  grand  conception  of  Copernicus 
that  this  earth  on  which  we  dwell  is  not  a  globe  fixed 
in  the  centre  of  the  universe,  but  is  simply  one  of  a 
number  of  bodies,  turning  on  their  own  axes  and  at 
the  same  time  moving  around  the  sun  as  a  centre. 
It  has  always  seemed  to  me  that  the  real  significance 
of  the  heliocentric  system  lies  in  the  greatness  of  this 
conception  rather  than  in  the  fact  of  the  discovery 
itself.  There  is  no  figure  in  astronomical  history 
which  may  more  appropriately  claim  the  admiration 
of  mankind  through  all  time  than  that  of  Copernicus. 
Scarcely  any  great  work  was  ever  so  exclusively  the 
work  of  one  man  as  was  the  heliocentric  system  the 
work  of  the  retiring  sage  of  Frauenburg.  No  more 
striking  contrast  between  the  views  of  scientific  re- 
search entertained  in  his  time  and  in  ours  can  be 
found  than  that  afforded  by  the  fact  that,  instead  of 
claiming  credit  for  his  great  work,  he  deemed  it 
rather  necessary  to  apologize  for  it  and,  so  far  as 
possible,  to  attribute  his  ideas  to  the  ancients. 

A  century  and  a  half  after  Copernicus  followed  the 
second  great  step,  that  taken  by  Newton.  This  was 
nothing  less  than  showing  that  the  seemingly  com- 


SIDE-LIGHTS    ON    ASTRONOMY 

plicated  and  inexplicable  motions  of  the  heavenly 
bodies  were  only  special  cases  of  the  same  kind  of 
motion,  governed  by  the  same  forces,  that  we  see 
around  us  whenever  a  stone  is  thrown  by  the  hand 
or  an  apple  falls  to  the  ground.  The  actual  motions 
of  the  heavens  and  the  laws  which  govern  them  being 
known,  man  had  the  key  with  which  he  might  com- 
mence to  unlock  the  mysteries  of  the  universe. 

When  Huyghens,  in  1656,  published  his  Sy sterna 
Saturnium,  where  he  first  set  forth  the  mystery  of 
the  rings  of  Saturn,  which,  for  nearly  half  a  century, 
had  perplexed  telescopic  observers,  he  prefaced  it 
with  a  remark  that  many,  even  among  the  learned, 
might  condemn  his  course  in  devoting  so  much  time 
and  attention  to  matters  far  outside  the  earth,  when 
he  might  better  be  studying  subjects  of  more  concern 
to  humanity.  Notwithstanding  that  the  inventor  of 
the  pendulum  clock  was,  perhaps,  the  last  astronomer 
against  whom  a  neglect  of  things  terrestrial  could 
be  charged,  he  thought  it  necessary  to  enter  into 
an  elaborate  defence  of  his  course  in  studying  the 
heavens.  Now,  however,  the  more  distant  objects 
are  in  space — I  might  almost  add  the  more  distant 
events  are  in  time — the  more  they  excite  the  atten- 
tion of  the  astronomer,  if  only  he  can  hope  to  acquire 
positive  knowledge  about  them.  Not,  however,  be- 
cause he  is  more  interested  in  things  distant  than  in 
things  near,  but  because  thus  he  may  more  com- 
pletely embrace  in  the  scope  of  his  work  the  beginning 
and  the  end,  the  boundaries  of  all  things,  and  thus, 
indirectly,  more  fully  comprehend  all  that  they  in- 
clude. From  his  stand -point, 

' '  All  are  but  parts  of  one  stupendous  whole, 

Whose  body  Nature  is  and  God  the  soul." 

260 


ASTRONOMICAL    KNOWLEDGE 

Others  study  Nature  and  her  plans  as  we  see  them 
developed  on  the  surface  of  this  little  planet  which 
we  inhabit ;  the  astronomer  would  fain  learn  the  plan 
on  which  the  whole  universe  is  constructed.  The 
magnificent  conception  of  Copernicus  is,  for  him, 
only  an  introduction  to  the  yet  more  magnificent 
conception  of  infinite  space  containing  a  collection 
of  bodies  which  we  call  the  visible  universe.  How 
far  does  this  universe  extend?  What  are  the  dis- 
tances and  arrangements  of  the  stars?  Does  the 
universe  constitute  a  system?  If  so,  can  we  com- 
prehend the  plan  on  which  this  system  is  formed,  of 
its  beginning  and  of  its  end  ?  Has  it  bounds  outside 
of  which  nothing  exists  but  the  black  and  starless 
depths  of  infinity  itself  ?  Or  are  the  stars  we  see  sim- 
ply such  members  of  an  infinite  collection  as  happen 
to  be  the  nearest  our  system  ?  A  few  such  questions 
as  these  we  are  perhaps  beginning  to  answer;  but 
hundreds,  thousands,  perhaps  even  millions,  of  years 
may  elapse  without  our  reaching  a  complete  solution. 
Yet  the  astronomer  does  not  view  them  as  Kantian 
antinomies,  in  the  nature  of  things  insoluble,  but  as 
questions  to  which  he  may  hopefully  look  for  at  least 
a  partial  answer. 

The  problem  of  the  distances  of  the  stars  is  of  pe- 
culiar interest  in  connection  with  the  Copernican 
system.  The  greatest  objection  to  this  system,  which 
must  have  been  more  clearly  seen  by  astronomers 
themselves  than  by  any  others,  was  found  in  the  ab- 
sence of  any  apparent  parallax  of  the  stars.  If  the 
earth  performed  such  an  immeasurable  circle  around 
the  sun  as  Copernicus  maintained,  then,  as  it  passed 
from  side  to  side  of  its  orbit,  the  stars  outside  the 
solar  system  must  appear  to  have  a  corresponding 

261 


SIDE-LIGHTS    ON    ASTRONOMY 

motion  in  the  other  direction,  and  thus  to  swing  back 
and  forth  as  the  earth  moved  in  one  and  the  other 
direction.  The  fact  that  not  the  slightest  swing  of 
that  sort  could  be  seen  was,  from  the  time  of  Ptolemy, 
the  basis  on  which  the  doctrine  of  the  earth's  im- 
mobility rested.  The  difficulty  was  not  grappled  with 
by  Copernicus  or  his  immediate  successors.  The 
idea  that  Nature  would  not  squander  space  by  al- 
lowing immeasurable  stretches  of  it  to  go  unused 
seems  to  have  been  one  from  which  medieval  think- 
ers could  not  entirely  break  away.  The  consideration 
that  there  could  be  no  need  of  any  such  economy, 
because  the  supply  was  infinite,  might  have  been 
theoretically  acknowledged,  but  was  not  practically 
felt.  The  fact  is  that  magnificent  as  was  the  concep- 
tion of  Copernicus,  it  was  dwarfed  by  the  conception 
of  stretches  from  star  to  star  so  vast  that  the  whole 
orbit  of  the  earth  was  only  a  point  in  comparison. 

An  indication  of  the  extent  to  which  the  difficulty 
thus  arising  was  felt  is  seen  in  the  title  of  a  book  pub- 
lished by  Horrebow,  the  Danish  astronomer,  some 
two  centuries  ago.  This. industrious  observer,  one  of 
the  first  who  used  an  instrument  resembling  our 
meridian  transit  of  the  present  day,  determined  to- 
see  if  he  could  find  the  parallax  of  the  stars  by  ob- 
serving the  intervals  at  which  a  pair  of  stars  in  oppo- 
site quarters  of  the  heavens  crossed  his  meridian  at 
opposite  seasons  of  the  year.  When,  as  he  thought, 
he  had  won  success,  he  published  his  observations 
and  conclusions  under  the  title  of  Copernicus  Trium- 
phans.  But  alas!  the  keen  criticism  of  his  successors 
showed  that  what  he  supposed  to  be  a  swing  of 
the  stars  from  season  to  season  arose  from  a  minute 
variation  in  the  rate  of  his  clock,  due  to  the  different 

262 


ASTRONOMICAL    KNOWLEDGE 

temperatures  to  which  it  was  exposed  during  the  day 
an<l  the  night.  The  measurement  of  the  distance 
even  of  the  nearest  stars  evaded  astronomical  re- 
search until  Bessel  and  Struve  arose  in  the  early 
part  of  the  present  century. 

On  some  aspects  of  the  problem  of  the  extent  of 
the  universe  light  is  being  thrown  even  now.  Evi- 
dence is  gradually  accumulating  which  points  to  the 
probability  that  the  successive  orders  of  smaller  and 
smaller  stars,  which  our  continually  increasing  tele- 
scopic power  brings  into  view,  are  not  situated  at 
greater  and  greater  distances,  but  that  we  actually 
see  the  boundary  of  our  universe.  This  indication 
lends  a  peculiar  interest  to  various  questions  grow- 
ing out  of  the  motions  of  the  stars.  Quite  possibly 
the  problem  of  these  motions  will  be  the  great  one  of 
the  future  astronomer.  Even  now  it  suggests  thoughts 
and  questions  of  the  most  far-reaching  character. 

I  have  seldom  felt  a  more  delicious  sense  of  repose 
than  when  crossing  the  ocean  during  the  summer 
months  I  sought  a  place  where  I  could  lie  alone  on 
the  deck,  look  up  at  the  constellations,  with  Lyra 
near  the  zenith,  and,  while  listening  to  the  clank  of 
the  engine,  try  to  calculate  the  hundreds  of  millions 
of  years  which  would  be  required  by  our  ship  to 
reach  the  star  a  Lyrae,  if  she  could  continue  her  course 
in  that  direction  without  ever  stopping.  It  is  a 
striking  example  of  how  easily  we  may  fail  to  realize 
our  knowledge  when  I  say  that  I  have  thought  many 
a  time  how  deliciously  one  might  pass  those  hundred 
millions  of  years  in  a  journey  to  the  star  a  Lyrae, 
without  its  occurring  to  me  that  we  are  actually 
making  that  very  journey  at  a  speed  compared  with 
which  the  motion  of  a  steamship  is  slow  indeed, 
is  263 


SIDE-LIGHTS    ON    ASTRONOMY 

Through  every  year,  every  hour,  every  minute,  of 
human  history  from  the  first  appearance  of  man  on 
the  earth,  from  the  era  of  the  builders  of  the  Pyra- 
mids, through  the  times  of  Caesar  and  Hannibal, 
through  the  period  of  every  event  that  history  re- 
cords, not  merely  our  earth,  but  the  sun  and  the 
whole  solar  system  with  it,  have  been  speeding  their 
way  towards  the  star  of  which  I  speak  on  a  journey 
of  which  we  know  neither  the  beginning  nor  the 
end.  We  are  at  this  moment  thousands  of  miles 
nearer  to  a  Lyrse  than  we  were  a  few  minutes  ago 
when  I  began  this  discourse,  and  through  every  future 
moment,  for  untold  thousands  of  years  to  come,  the 
earth  and  all  there  is  on  it  will  be  nearer  to  a  Lyrae, 
or  nearer  to  the  place  where  that  star  now  is,  by 
hundreds  of  miles  for  every  minute  of  time  come  and 
gone.  When  shall  we  get  there?  Probably  in  less 
than  a  million  years,  perhaps  in  half  a  million.  We 
cannot  tell  exactly,  but  get  there  we  must  if  the  laws 
of  nature  and  the  laws  of  motion  continue  as  they  are. 
To  attain  to  the  stars  was  the  seemingly  vain  wish 
of  an  ancient  philosopher,  but  the  whole  human  race 
is,  in  a  certain  sense,  realizing  this  wish  as  rapidly  as 
a  speed  of  ten  miles  a  second  can  bring  it  about. 

I  have  called  attention  to  this  motion  because  it 
may,  in  the  not  distant  future,  afford  the  means  of 
approximating  to  a  solution  of  the  problem  already 
mentioned — that  of  the  extent  of  the  universe.  Not- 
withstanding the  success  of  astronomers  during  the 
present  century  in  measuring  the  parallax  of  a  num- 
ber of  stars,  the  most  recent  investigations  show  that 
there  are  very  few,  perhaps  hardly  more  than  a  score, 
of  stars  of  which  the  parallax,  and  therefore  the  dis- 
tance, has  been  determined  with  any  approach  to 

264 


ASTRONOMICAL    KNOWLEDGE 

certainty.  Many  parallaxes  determined  about  the 
middle  of  the  nineteenth  century  have  had  to  dis- 
appear before  the  powerful  tests  applied  by  measures 
with  the  heliometer ;  others  have  been  greatly  reduced 
and  the  distances  of  the  stars  increased  in  proportion. 
So  far  as  measurement  goes,  we  can  only  say  of  the 
distances  of  all  the  stars,  except  the  few  whose  paral- 
laxes have  been  determined,  that  they  are  immeas- 
urable, The  radius  of  the  earth's  orbit,  a  line  more 
than  ninety  millions  of  miles  in  length,  not  only 
vanishes  from  sight  before  we  reach  the  distance  of 
the  great  mass  of  stars,  but  becomes  such  a  mere 
point  that  when  magnified  by  the  powerful  instru- 
ments of  modern  times  the  most  delicate  appliances 
fail  to  make  it  measurable.  Here  the  solar  motion 
comes  to  our  help.  This  motion,  by  which,  as  I 
have  said,  we  are  carried  unceasingly  through  space, 
is  made  evident  by  a  motion  of  most  of  the  stars  in 
the  opposite  direction,  just  as  passing  through  a 
country  on  a  railway  we  see  the  houses  on  the  right 
and  on  the  left  being  left  behind  us.  It  is  clear 
enough  that  the  apparent  motion  will  be  more  rapid 
the  nearer  the  object.  We  may  therefore  form  some 
idea  of  the  distance  of  the  stars  when  we  know  the 
amount  of  the  motion.  It  is  found  that  in  the  great 
mass  of  stars  of  the  sixth  magnitude,  the  smallest 
visible  to  the  naked  eye,  the  motion  is  about  three 
seconds  per  century.  As  a  measure  thus  stated  does 
not  convey  an  accurate  conception  of  magnitude  to 
one  not  practised  in  the  subject,  I  would  say  that  in 
the  heavens,  to  the  ordinary  eye,  a  pair  of  stars  will 
appear  single  unless  they  are  separated  by  a  distance 
of  150  or  200  seconds.  Let  us,  then,  imagine  our- 
selves looking  at  a  star  of  the  sixth  magnitude,  which 

265 


SIDE-LIGHTS    ON    ASTRONOMY 

is  at  rest  while  we  are  carried  past  it  with  the  motion 
of  six  to  eight  miles  per  second  which  I  have  described. 
Mark  its  position  in  the  heavens  as  we  see  it  to-day; 
then  let  its  position  again  be  marked  five  thousand 
years  hence.  A  good  eye  will  just  be  able  to  perceive 
that  there  are  two  stars  marked  instead  of  one.  The 
two  would  be  so  close  together  that  no  distinct  space 
between  them  could  be  perceived  by  unaided  vision. 
It  is  due  to  the  magnifying  power  of  the  telescope, 
enlarging  such  small  apparent  distances,  that  the 
motion  has  been  determined  in  so  small  a  period  as 
the  one  hundred  and  fifty  years  during  which  accurate 
observations  of  the  stars  have  been  made. 

The  motion  just  described  has  been  fairly  well 
determined  for  what,  astronomically  speaking,  are 
the  brighter  stars ;  that  is  to  say,  those  visible  to  the 
naked  eye.  But  how  is  it  with  the  millions  of  faint 
telescopic  stars,  especially  those  which  form  the 
cloud  masses  of  the  Milky  Way?  The  distance  of 
these  stars  is  undoubtedly  greater,  and  the  apparent 
motion  is  therefore  smaller.  Accurate  observations 
upon  such  stars  have  been  commenced  only  recently, 
so  that  we  have  not  yet  had  time  to  determine  the 
amount  of  the  motion.  But  the  indication  seems  to 
be  that  it  will  prove  quite  a  measurable  quantity  and 
that  before  the  twentieth  century  has  elapsed,  it  will 
be  determined  for  very  much  smaller  stars  than  those 
which  have  heretofore  been  studied.  A  photographic 
chart  of  the  whole  heavens  is  now  being  constructed 
by  an  association  of  observatories  in  some  of  the 
leading  countries  of  the  world.  I  cannot  say  all  the 
leading  countries,  because  then  we  should  have  to 
exclude  our  own,  which,  unhappily,  has  taken  no 
part  in  this  work.  At  the  end  of  the  twentieth  cen- 

266 


ASTRONOMICAL    KNOWLEDGE 

tury  we  may  expect  that  the  work  Avill  be  repeated. 
Then,  by  comparing  the  charts,  we  shall  see  the  effect 
of  the  solar  motion  and  perhaps  get  new  light  upon 
the  problem  in  question. 

Closely  connected  with  the  problem  of  the  extent 
of  the  universe  is  another  which  appears,  for  us,  to 
be  insoluble  because  it  brings  us  face  to  face  with 
infinity  itself.  We  are  familiar  enough  with  eternity, 
or,  let  us  say,  the  millions  or  hundreds  of  millions  of 
years  which  geologists  tell  us  must  have  passed  while 
the  crust  of  the  earth  was  assuming  its  present  form, 
our  mountains  being  built,  our  rocks  consolidated, 
and  successive  orders  of  animals  coming  and  going. 
Hundreds  of  millions  of  years  is  indeed  a  long  time, 
and  yet,  when  we  contemplate  the  changes  supposed 
to  have  taken  place  during  that  time,  we  do  not  look 
out  on  eternity  itself,  which  is  veiled  from  our  sight, 
as  it  were,  by  the  unending  succession  of  changes 
that  mark  the  progress  of  time.  But  in  the  motions 
of  the  stars  we  are  brought  face  to  face  with  eternity 
and  infinity,  covered  by  no  veil  whatever.  It  would 
be  bold  to  speak  dogmatically  on  a  subject  where  the 
springs  of  being  are  so  far  hidden  from  mortal  eyes 
as  in  the  depths  of  the  universe.  But,  without  de- 
claring its  positive  certainty,  it  must  be  said  that  the 
conclusion  seems  unavoidable  that  a  number  of  stars 
are  moving  with  a  speed  such  that  the  attraction  of 
all  the  bodies  of  the  universe  could  never  stop  them. 
One  such  case  is  that  of  Arcturus,  the  bright  reddish 
star  familiar  to  mankind  since  the  days  of  Job,  and 
visible  near  the  zenith  on  the  clear  evenings  of  May 
and  June.  Yet  another  case  is  that  of  a  star  known 
in  astronomical  nomenclature  as  1830  Groombridge, 
which  exceeds  all  others  in  its  angular  proper  motion 

267 


SIDE-LIGHTS    ON    ASTRONOMY 


as  seen  from  the  earth.  We  should  naturally  sup- 
pose that  it  seems  to  move  so  fast  because  it  is  near 
us.  But  the  best  measurements  of  its  parallax  seem 
to  show  that  it  can  scarcely  be  less  than  two  million 
times  the  distance  of  the  earth  from  the  sun,  while 
it  may  be  much  greater.  Accepting  this  result,  its 
velocity  cannot  be  much  less  than  two  hundred  miles 
per  second,  and  may  be  much  more.  With  this  speed 
it  would  make  the  circuit  of  our  globe  in  two  minutes, 
and  had  it  gone  round  and  round  in  our  latitudes  we 
should  have  seen  it  fly  past  us  a  number  of  times 
since  I  commenced  this  discourse.  It  would  make 
the  journey  from  the  earth  to  the  sun  in  five  days. 
If  it  is  now  near  the  centre  of  our  universe  it  would 
probably  reach  its  confines  in  a  million  of  years.  So 
far  as  our  knowledge  goes,  there  is  no  force  in 
nature  which  would  ever  have  set  it  in  motion  and 
no  force  which  can  ever  stop  it.  What,  then,  was 
the  history  of  this  star,  and,  if  there  are  planets  cir- 
culating around,  what  the  experience  of  beings  who 
may  have  lived  on  those  planets  during  the  ages  which 
geologists  and  naturalists  assure  us  our  earth  has 
existed  ?  Was  there  a  period  when  they  saw  at  night 
only  a  black  and  starless  heaven  ?  Was  there  a  time 
when  in  that  heaven  a  small  faint  patch  of  light  began 
gradually  to  appear?  Did  that  patch  of  light  grow 
larger  and  larger  as  million  after  million  of  years 
elapsed  ?  Did  it  at  last  fill  the  heavens  and  break  up 
into  constellations  as  we  now  see  them  ?  As  millions 
more  of  years  elapse  will  the  constellations  gather  to- 
gether in  the  opposite  quarter  and  gradually  diminish 
to  a  patch  of  light  as  the  star  pursues  its  irresistible 
course  of  two  hundred  miles  per  second  through  the 
wilderness  of  space,  leaving  our  universe  farther  and 

268 


ASTRONOMICAL    KNOWLEDGE 

farther  behind  it,  until  it  is  lost  in  the  distance  ?  If 
the  conceptions  of  modern  science  are  to  be  consid- 
ered as  good  for  all  time — a  point  on  which  I  confess 
to  a  large  measure  of  scepticism — then  these  questions 
must  be  answered  in  the  affirmative. 

The  problems  of  which  I  have  so  far  spoken  are 
those  of  what  may  be  called  the  older  astronomy. 
If  I  apply  this  title  it  is  because  that  branch  of  the 
science  to  which  the  spectroscope  has  given  birth  is 
often  called  the  new  astronomy.  It  is  commonly 
to  be  expected  that  a  new  and  vigorous  form  of  scien- 
tific research  will  supersede  that  which  is  hoary  with 
antiquity.  But  I  am  not  willing  to  admit  that  such 
is  the  case  with  the  old  astronomy,  if  old  we  may  call 
it.  It  is  more  pregnant  with  future  discoveries  to- 
day than  it  ever  has  been,  and  it  is  more  disposed  to 
welcome  the  spectroscope  as  a  useful  handmaid, 
which  may  help  it  on  to  new  fields,  than  it  is  to  give 
way  to  it.  How  useful  it  may  thus  become  has  been 
recently  shown  by  a  Dutch  astronomer,  who  finds 
that  the  stars  having  one  type  of  spectrum  belong 
mostly  to  the  Milky  Way,  and  are  farther  from  us 
than  the  others. 

In  the  field  of  the  newer  astronomy  perhaps  the 
most  interesting  work  is  that  associated  with  comets. 
It  must  be  confessed,  however,  that  the  spectroscope 
has  rather  increased  than  diminished  the  mystery 
which,  in  some  respects,  surrounds  the  constitution 
of  these  bodies.  The  older  astronomy  has  satis- 
factorily accounted  for  their  appearance,  and  we 
might  also  say  for  their  origin  and  their  end,  so  far 
as  questions  of  origin  can  come  into  the  domain  of 
science.  It  is  now  known  that  comets  are  not  wan- 
derers through  the  celestial  spaces  from  star  to  star, 

269 


SIDE-LIGHTS    ON    ASTRONOMY 

but  must  always  have  belonged  to  our  system.  But 
their  orbits  are  so  very  elongated  that  thousands,  or 
even  hundreds  of  thousands,  of  years  are  required  for 
a  revolution.  Sometimes,  however,  a  comet  passing 
near  to  Jupiter  is  so  fascinated  by  that  planet  that, 
in  its  vain  attempts  to  follow  it,  it  loses  so  much  of 
its  primitive  velocity  as  to  circulate  around  the  sun 
in  a  period  of  a  few  years,  and  thus  to  become,  ap- 
parently, a  new  member  of  our  system.  If  the  orbit 
of  such  a  comet,  or  in  fact  of  any  comet,  chances  to 
intersect  that  of  the  earth,  the  latter  in  passing  the 
point  of  intersection  encounters  minute  particles 
which  cause  a  meteoric  shower. 

But  all  this  does  not  tell  us  much  about  the  nature 
and  make-up  of  a  comet.  Does  it  consist  of  nothing 
but  isolated  particles,  or  is  there  a  solid  nucleus,  the 
attraction  of  which  tends  to  keep  the  mass  together  ? 
No  one  yet  knows.  The  spectroscope,  if  we  interpret 
its  indications  in  the  usual  way,  tells  us  that  a  comet 
is  simply  a  mass  of  hydrocarbon  vapor,  shining  by 
its  own  light.  But  there  must  be  something  wrong 
in  this  interpretation.  That  the  light  is  reflected 
sunlight  seems  to  follow  necessarily  from  the  increased 
brilliancy  of  the  comet  as  it  approaches  the  sun  and 
its  disappearance  as  it  passes  away. 

Great  attention  has  recently  been  bestowed  upon 
the  physical  constitution  of  the  planets  and  the 
changes  which  the  surfaces  of  those  bodies  may  un- 
dergo. In  this  department  of  research  we  must  feel 
gratified  by  the  energy  of  our  countrymen  who  have 
entered  upon  it.  Should  I  seek  to  even  mention  all 
the  results  thus  made  known  I  might  be  stepping 
on  dangerous  ground,  as  many  questions  are  still 
unsettled.  While  every  astronomer  has  entertained 

270 


ASTRONOMICAL    KNOWLEDGE 

the  highest  admiration  for  the  energy  and  enthusiasm 
shown  by  Mr.  Percival  Lowell  in  founding  an  observa- 
tory in  regions  where  the  planets  can  be  studied  under 
the  most  favorable  conditions,  they  cannot  lose  sight 
of  the  fact  that  the  ablest  and  most  experienced  ob- 
servers are  liable  to  error  when  they  attempt  to  de- 
lineate the  features  of  a  body  50,000,000  or  100,000,- 
ooo  miles  away  through  such  a  disturbing  medium 
as  our  atmosphere.  Even  on  such  a  subject  as  the 
canals  of  Mars  doubts  may  still  be  felt.  That  cer- 
tain markings  to  which  Schiaparelli  gave  the  name 
of  canals  exist,  few  will  question.  But  it  may  be 
questioned  whether  these  markings  are  the  fine,  sharp, 
uniform  lines  found  on  Schiaparelli's  map  and  de- 
lineated in  Lowell's  beautiful  book.  It  is  certainly 
curious  that  Barnard  at  Mount  Hamilton,  with  the 
most  powerful  instrument  and  under  the  most  fa- 
vorable circumstances,  does  not  see  these  markings 
as  canals. 

I  can  only  mention  among  the  problems  of  the 
spectroscope  the  elegant  and  remarkable  solution  of 
the  mystery  surrounding  the  rings  of  Saturn,  which 
has  been  effected  by  Keeler  at  Allegheny.  That  these 
rings  could  not  be  solid  has  long  been  a  conclusion 
of  the  laws  of  mechanics,  but  Keeler  was  the  first  to 
show  that  they  really  consist  of  separate  particles, 
because  the  inner  portions  revolve  more  rapidly  than 
the  outer. 

The  question  of  the  atmosphere  of  Mars  has  also 
received  an  important  advance  by  the  work  of  Camp- 
bell at  Mount  Hamilton.  Although  it  is  not  proved 
that  Mars  has  no  atmosphere,  for  the  existence  of 
some  atmosphere  can  scarcely  be  doubted,  yet  the 
Mount  Hamilton  astronomer  seems  to  have  shown, 

271 


SIDE-LIGHTS    ON    ASTRONOMY 

with  great  conclusiveness,  that  it  is  so  rare  as  not  to 
produce  any  sensible  absorption  of  the  solar  rays. 

I  have  left  an  important  subject  for  the  close.  It 
belongs  entirely  to  the  older  astronomy,  and  it  is 
one  with  which  I  am  glad  to  say  this  observatory  is 
expected  to  especially  concern  itself.  I  refer  to  the 
question  of  the  variation  of  latitudes,  that  singular 
phenomenon  scarcely  suspected  ten  years  ago,  but 
brought  out  by  observations  in  Germany  during  the 
past  eight  years,  and  reduced  to  law  with  such  brill- 
iant success  by  our  own  Chandler.  The  north  pole 
is  not  a  fixed  point  on  the  earth's  surface,  but  moves 
around  in  rather  an  irregular  way.  True,  the  motion 
is  small ;  a  circle  of  sixty  feet  in  diameter  will  include 
the  pole  in  its  widest  range.  This  is  a  very  small  mat- 
ter so  far  as  the  interests  of  daily  life  are  concerned ; 
but  it  is  very  important  to  the  astronomer.  It  is 
not  simply  a  motion  of  the  pole  of  the  earth,  but  a 
wabbling  of  the  solid  earth  itself.  No  one  knows 
what  conclusions  of  importance  to  our  race  may  yet 
follow  from  a  study  of  the  stupendous  forces  neces- 
sary to  produce  even  this  slight  motion. 

The  director  of  this  new  observatory  has  already 
distinguished  himself  in  the  delicate  and  difficult  work 
of  investigating  this  motion,  and  I  am  glad  to  know 
that  he  is  continuing  the  work  here  with  one  of  the 
finest  instruments  ever  used  for  the  purpose,  a  splen- 
did product  of  American  mechanical  genius.  I  can 
assure  you  that  astronomers  the  world  over  will  look 
with  the  greatest  interest  for  Professor  Doolittle's 
success  in  the  arduous  task  he  has  undertaken. 

There  is  one  question  connected  with  these  studies 
of  the  universe  on  which  I  have  not  touched,  and 
which  is,  nevertheless,  of  transcendent  interest. 

272 


ASTRONOMICAL    KNOWLEDGE 

What  sort  of  life,  spiritual  and  intellectual,  exists  in 
distant  worlds  ?  We  cannot  for  a  moment  suppose  that 
our  little  planet  is  the  only  one  throughout  the  whole 
universe  on  which  may  be  found  the  fruits  of  civiliza- 
tion, family  affection,  friendship,  the  desire  to  pene- 
trate the  mysteries  of  creation.  And  yet  this  question 
is  not  to-day  a  problem  of  astronomy,  nor  can  we  see 
any  prospect  that  it  ever  will  be,  for  the  simple  reason 
that  science  affords  us  no  hope  of  an  answer  to  any 
question  that  we  may  send  through  the  fathomless 
abyss.  When  the  spectroscope  was  in  its  infancy 
it  was  suggested  that  possibly  some  difference  might 
be  found  in  the  rays  reflected  from  living  matter, 
especially  from  vegetation,  that  might  enable  us  to 
distinguish  them  from  rays  reflected  by  matter  not 
endowed  with  life.  But  this  hope  has  not  been 
realized,  nor  does  it  seem  possible  to  realize  it.  The 
astronomer  cannot  afford  to  waste  his  energies  on 
hopeless  speculation  about  matters  of  which  he 
cannot  learn  anything,  and  he  therefore  leaves  this 
question  of  the  plurality  of  worlds  to  others  who  are 
as  competent  to  discuss  it  as  he  is.  All  he  can  tell 
the  world  is: 

He  who  through  vast  immensity  can  pierce, 
See  worlds  on  worlds  compose  one  universe; 
Observe  how  system  into  system  runs, 
What  other  planets  circle  other  suns, 
What  varied  being  peoples  every  star, 
May  tell  why  Heaven  has  made  us  as  we  are. 


XVIII 
ASPECTS   OF   AMERICAN   ASTRONOMY* 

THE    University  of    Chicago    yesterday  accepted 
one  of  the  most  munificent  gifts  ever  made  for 
the  promotion  of  any  single  science,  and  with  appro- 
priate ceremonies  dedicated  it  to  the  increase  of  our 
knowledge  of  the  heavenly  bodies. 

The  president  of  your  university  has  done  me  the 
honor  of  inviting  me  to  supplement  what  was  said  on 
that  occasion  by  some  remarks  of  a  more  general 
nature  suggested  by  the  celebration.  One  is  natural- 
ly disposed  to  say  first  what  is  uppermost  in  his  mind. 
At  the  present  moment  this  will  naturally  be  the  gen- 
eral impression  made  by  what  has  been  seen  and 
heard.  The  ceremonies  were  attended,  not  only  by 
a  remarkable  delegation  of  citizens,  but  by  a  number 
of  visiting  astronomers  which  seems  large  when  we 
consider  that  the  profession  itself  is  not  at  all  nu- 
merous in  any  country.  As  one  of  these,  your  guests, 
I  am  sure  that  I  give  expression  only  to  their  unani- 
mous sentiment  in  saying  that  we  have  been  ex- 
tremely gratified  in  many  ways  by  all  that  we  have 
seen  and  heard.  The  mere  fact  of  so  munificent  a 
gift  to  science  cannot  but  excite  universal  admiration. 

*  Address  delivered  at  the  University  of  Chicago,  October  22, 
1897,  in  connection  with  the  dedication  of  the  Yerkes  Observa- 
tory. Printed  in  the  Astrophysical  Journal.  November,  1897. 

274 


ASPECTS    OF    AMERICAN    ASTRONOMY 

We  knew  well  enough  that  it  was  nothing  more  than 
might  have  been  expected  from  the  public  spirit  of 
this  great  West ;  but  the  first  view  of  a  towering  snow- 
peak  is  none  the  less  impressive  because  you  have 
learned  in  your  geography  how  many  feet  high  it  is, 
and  great  acts  are  none  the  less  admirable  because 
they  correspond  to  what  you  have  heard  and  read, 
and  might  therefore  be  led  to  expect. 

The  next  gratifying  feature  is  the  great  public  in- 
terest excited  by  the  occasion.  That  the  opening  of 
a  purely  scientific  institution  should  have  led  so  large 
an  assemblage  of  citizens  to  devote  an  entire  day, 
including  a  long  journey  by  rail,  to  the  celebration 
of  yesterday  is  something  most  suggestive  from  its 
unfamiliarity.  A  great  many  scientific  establish- 
ments have  been  inaugurated  during  the  last  half- 
century,  but  if  on  any  such  occasion  so  large  a  body 
of  citizens  has  gone  so  great  a  distance  to  take  part 
in  the  inauguration,  the  fact  has  at  the  moment  es- 
caped my  mind. 

That  the  interest  thus  shown  is  not  confined  to  the 
hundreds  of  attendants,  but  must  be  shared  by  your 
great  public,  is  shown  by  the  unfailing  barometer  of 
journalism.  Here  we  have  a  field  in  which  the  non- 
survival  of  the  unfit  is  the  rule  in  its  most  ruthless 
form.  The  journals  that  we  see  and  read  are  merely 
the  fortunate  few  of  a  countless  number,  dead  and 
forgotten,  that  did  not  know  what  the  public  wanted 
to  read  about.  The  eagerness  shown  by  the  repre- 
sentatives of  your  press  in  recording  everything  your 
guests  would  say  was  accomplished  by  an  enterprise 
in  making  known  everything  that  occurred,  and,  in 
case  of  an  emergency  requiring  a  heroic  measure, 
what  did  not  occur,  showing  that  smart  journalists 

275 


SIDE-LIGHTS    ON    ASTRONOMY 

of  the  East  must  have  learned  their  trade,  or  at  least 
breathed  their  inspiration,  in  these  regions.  I  think 
it  was  some  twenty  years  since  I  told  a  European 
friend  that  the  eighth  wonder  of  the  world  was  a 
Chicago  daily  newspaper.  Since  that  time  the  course 
of  journalistic  enterprise  has  been  in  the  reverse  di- 
rection to  that  of  the  course  of  empire,  eastward  in- 
stead of  westward. 

It  has  been  sometimes  said — wrongfully,  I  think — 
that  scientific  men  form  a  mutual  admiration  society. 
One  feature  of  the  occasion  made  me  feel  that  we, 
your  guests,  ought  then  and  there  to  have  organized 
such  a  society  and  forthwith  proceeded  to  business. 
This  feature  consisted  in  the  conferences  on  almost 
every  branch  of  astronomy  by  which  the  celebration 
of  yesterday  was  preceded.  The  fact  that  beyond 
the  acceptance  of  a  graceful  compliment  I  contrib- 
uted nothing  to  these  conferences  relieves  me  from 
the  charge  of  bias  or  self-assertion  in  saying  that  they 
gave  me  a  new  and  most  inspiring  view  of  the  energy 
now  being  expended  in  research  by  the  younger  gen- 
eration of  astronomers.  All  the  experience  of  the 
past  leads  us  to  believe  that  this  energy  will  reap 
the  reward  which  nature  always  bestows  upon  those 
who  seek  her  acquaintance  from  unselfish  motives. 
In  one  way  it  might  appear  that  little  was  to  be 
learned  from  a  meeting  like  that  of  the  present  week. 
Each  astronomer  may  know  by  publications  pertain- 
ing to  the  science  what  all  the  others  are  doing.  But 
knowledge  obtained  in  this  way  has  a  sort  of  ab- 
stractness  about  it  a  little  like  our  knowledge  of  the 
progress  of  civilization  in  Japan,  or  of  the  great  ex- 
tent of  the  Australian  continent.  It  was,  therefore, 
a  most  happy  thought  on  the  part  of  your  authorities 

276 


ASPECTS    OF    AMERICAN    ASTRONOMY 

to  bring  together  the  largest  possible  number  of  visit- 
ing astronomers  from  Europe,  as  well  as  America,  in 
order  that  each  might  see,  through  the  attrition  of 
personal  contact,  what  progress  the  others  were  mak- 
ing in  their  researches.  To  the  visitors  at  least  I  am 
sure  that  the  res*ult  of  this  meeting  has  been  extremely 
gratifying.  They  earnestly  hope,  one  and  all,  that 
the  callers  of  the  conference  will  not  themselves  be 
more  disappointed  in  its  results ;  that,  however  little 
they  may  have  actually  to  learn  of  methods  and  re- 
sults, they  will  feel  stimulated  to  well-directed  efforts 
and  find  themselves  inspired  by  thoughts  which,  how- 
ever familiar,  will  now  be  more  easily  worked  out. 

We  may  pass  from  the  aspects  of  the  case  as  seen 
by  the  strictly  professional  class  to  those  general 
aspects  fitted  to  excite  the  attention  of  the  great 
public.  From  the  point  of  view  of  the  latter  it  may 
well  appear  that  the  most  striking  feature  of  the 
celebration  is  the  great  amount  of  effort  which  is 
shown  to  be  devoted  to  the  cultivation  of  a  field  quite 
outside  the  ordinary  range  of  human  interests.  The 
workers  whom  we  see  around  us  are  only  a  detach- 
ment from  an  army  of  investigators  who,  in  many 
parts  of  the  world,  are  seeking  to  explore  the  mys- 
teries of  creation.  Why  so  great  an  expenditure  of 
energy  ?  Certainly  not  to  gain  wealth,  for  astronomy 
is  perhaps  the  one  field  of  scientific  work  which,  in  our 
expressive  modern  phrase,  "has  no  money  in  it."  It 
is  true  that  the  great  practical  use  of  astronomical 
science  to  the  country  and  the  world  in  affording  us 
the  means  of  determining  positions  on  land  and  at 
sea  is  frequently  pointed  out.  It  is  said  that  an 
Astronomer  Royal  of  England  once  calculated  that 
every  meridian  observation  of  the  moon  made  at 

277 


SIDE-LIGHTS    ON    A'STRONOMY 

Greenwich  was  worth  a  pound  sterling,  on  account  of 
the  help  it  would  afford  to  the  navigation  of  the  ocean. 
An  accurate  map  of  the  United  States  cannot  be  con- 
structed without  astronomical  observations  at  nu- 
merous points  scattered  over  the  \vhole  country,  aided 
by  data  which  great  observatories  have  been  accumu- 
lating for  more  than  a  century,  and  must  continue 
to  accumulate  in  the  -future. 

But  neither  the  measurement  of  the  earth,  the 
making  of  maps,  nor  the  aid  of  the  navigator  is  the 
main  object  which  the  astronomers  of  to-day  have 
in  view.  If  they  do  not  quite  share  the  sentiment  of 
that  eminent  mathematician,  who  is  said  to  have 
thanked  God  that  his  science  was  one  which  could 
not  be  prostituted  to  any  useful  purpose,  they  still 
know  well  that  to  keep  utilitarian  objects  in  view 
would  only  prove  a  handicap  on  their  efforts.  Con- 
sequently they  never  ask  in  what  way  their  science 
is  going  to  benefit  mankind.  As  the  great  captain 
of  industry  is  moved  by  the  love  of  wealth,  and  the 
political  leader  by  the  love  of  power  over  men,  so  the 
astronomer  is  moved  by  the  love  of  knowledge  for  its 
own  sake,  and  not  for  the  sake  of  its  useful  applica- 
tions. Yet  he  is  proud  to  know  that  his  science  has 
been  worth  more  to  mankind  than  it  has  cost.  He 
does  not  value  its  results  merely  as  a  means  of  cross- 
ing the  ocean  or  mapping  the  country,  for  he  feels 
that  man  does  not  live  by  bread  alone.  If  it  is  not 
more  than  bread  to  know  the  place  we  occupy  in  the 
universe,  it  is  certainly  something  which  we  should 
place  not  far  behind  the  means  of  subsistence.  That 
we  now  look  upon  a  comet  as  something  very  inter- 
esting, of  which  the  sight  affords  us  a  pleasure  un- 
mixed with  fear  of  war,  pestilence,  or  other  calamity, 

278 


ASPECTS    OF   AMERICAN    ASTRONOMY 

and  of  which  we  therefore  wish  the  return,  is  a  gain 
we  cannot  measure  by  money.  In  all  ages  astronomy 
has  been  an  index  to  the  civilization  of  the  people  who 
cultivated  it.  It  has  been  crude  or  exact,  enlightened 
or  mingled  with  superstition,  according  to  the  current 
mode  of  thought.  When  once  men  understand  the 
relation  of  the  planet  on  which  they  dwell  to  the  uni- 
verse at  large,  superstition  is  doomed  to  speedy  extinc- 
tion. This  alone  is  an  object  worth  more  than  money. 
Astronomy  may  fairly  claim  to  be  that  science 
which  transcends  all  others  in  its  demands  upon  the 
practical  application  of  our  reasoning  powers.  Look 
at  the  stars  that  stud  the  heavens  on  a  clear  evening. 
What  more  hopeless  problem  to  one  confined  to 
earth  than  that  of  determining  their  varying  dis- 
tances, their  motions,  and  their  physical  constitu- 
tion? Everything  on  earth  we  can  handle  and  in- 
vestigate. But  how  investigate  that  which  is  ever 
beyond  our  reach,  on  which  we  can  never  make  an 
experiment?  On  certain  occasions  we  see  the  moon 
pass  in  front  of  the  sun  and  hide  it  from  our  eyes. 
To  an  observer  a  few  miles  away  the  sun  was  not 
entirely  hidden,  for  the  shadow  of  the  moon  in  a 
total  eclipse  is  rarely  one  hundred  miles  wide.  On 
another  continent  no  eclipse  at  all  may  have  been 
visible.  Who  shall  take  a  map  of  the  world  and 
mark  upon  it  the  line  on  which  the  moon's  shadow 
will  travel  during  some  eclipse  a  hundred  years 
hence  ?  Who  shall  map  out  the  orbits  of  the  heaven- 
ly bodies  as  they  are  going  to  appear  in  a  hundred 
thousand  years?  How  shall  we  ever  know  of  what 
chemical  elements  the  sun  and  the  stars  are  made? 
All  this  has  been  done,  but  not  by  the  intellect  of 
any  one  man.  The  road  to  the  stars  has  been  opened 

10  279 


SIDE-LIGHTS     ON    ASTRONOMY 

only  by  the  efforts  of  many  generations  of  mathe- 
maticians and  observers,  each  of  whom  began  where 
his  predecessor  had  left  off. 

We  have  reached  a  stage  where  we  know  much  of 
the  heavenly  bodies.  We  have  mapped  out  our 
solar  system  with  great  precision.  But  how  with 
that  great  universe  of  millions  of  stars  in  which  our 
solar  system  is  only  a  speck  of  star -dust,  a  speck 
which  a  traveller  through  the  wilds  of  space  might 
pass  a  hundred  times  without  notice?  We  have 
learned  much  about  this  universe,  though  our  knowl- 
edge of  it  is  still  dim.  We  see  it  as  a  traveller  on  a 
mountain-top  sees  a  distant  city  in  a  cloud  of  mist, 
by  a  few  specks  of  glimmering  light  from  steeples  or 
roofs.  We  want  to  know  more  about  it,  its  origin 
and  its  destiny ;  its  limits  in  time  and  space,  if  it  has 
any ;  what  function  it  serves  in  the  universal  economy. 
The  journey  is  long,  yet  we  want,  in  knowledge  at 
least,  to  make  it.  Hence  we  build  observatories  and 
train  observers  and  investigators.  Slow,  indeed,  is 
progress  in  the  solution  of  the  greatest  of  problems, 
when  measured  by  what  we  want  to  know.  Some 
questions  may  require  centuries,  others  thousands  of 
years  for  their  answer.  And  yet  never  was  progress 
more  rapid  than  during  our  time.  In  some  directions 
our  astronomers  of  to-day  are  out  of  sight  of  those 
of  fifty  years  ago ;  we  are  even  gaining  heights  which 
twenty  years  ago  looked  hopeless.  Never  before  had 
the  astronomer  so  much  work — good,  hard,  yet  hope- 
ful work — before  him  as  to-day.  He  who  is  leaving 
the  stage  feels  that  he  has  only  begun  and  must 
leave  his  successors  with  more  to  do  than  his  pred- 
ecessors left  him. 

To  us  an  interesting  feature  of  this  progress  is  the 

280 


ASPECTS    OF    AMERICAN    ASTRONOMY 

part  taken  in  it  by  our  own  country.  The  science  of 
our  day,  it  is  true,  is  of  no  country.  Yet  we  very 
appropriately  speak  of  American  science  from  the 
fact  that  our  traditional  reputation  has  not  been 
that  of  a  people  deeply  interested  in  the  higher 
branches  of  intellectual  work.  Men  yet  living  can 
remember  when  in  the  eyes  of  the  universal  church 
of  learning,  all  cisatlantic  countries,  our  own  included, 
were  paries  infidelmm. 

Yet  American  astronomy  is  not  entirely  of  our 
generation.  In  the  middle  of  the  last  century  Pro- 
fessor Winthrop,  of  Harvard,  was  an  industrious  ob- 
server of  eclipses  and  kindred  phenomena,  whose  work 
was  recorded  in  the  transactions  of  learned  societies. 
But  the  greatest  astronomical  activity  during  our 
colonial  period  was  that  called  out  by  the  transit  of 
Venus  in  1769,  which  was  visible  in  this  country.  A 
committee  of  the  American  Philosophical  Society,  at 
Philadelphia,  organized  an  excellent  system  of  ob- 
servations, which  we  now  know  to  have  been  fully 
as  successful,  perhaps  more  so,  than  the  majority  of 
those  made  on  other  continents,  owing  mainly  to  the 
advantages  of  air  and  climate.  Among  the  ob- 
servers wras  the  celebrated  Rittenhouse,  to  whom  is 
due  the  distinction  of  having  been  the  first  American 
astronomer  whose  work  has  an  important  place  in 
the  history  of  the  science.  In  addition  to  the  ob- 
servations which  he  has  left  us,  he  was  the  first  in- 
ventor or  proposer  of  the  collimating  telescope,  an 
instrument  which  has  become  almost  a  necessity 
wherever  accurate  observations  are  made.  The  fact 
that  the  subsequent  invention  by  Bessel  may  have 
been  independent  does  not  detract  from  the  merits  of 
either. 

281 


SIDE-LIGHTS    ON    ASTRONOMY 

Shortly  after  the  transit  of  Venus,  which  I  have 
mentioned,  the  war  of  the  Revolution  commenced. 
The  generation  which  carried  on  that  war  and  the 
following  one,  which  framed  our  Constitution  and 
laid  the  bases  of  our  political  institutions,  were 
naturally  too  much  occupied  with  these  great  prob- 
lems to  pay  much  attention  to  pure  science.  While 
the  great  mathematical  astronomers  of  Europe  were 
laying  the  foundation  of  celestial  mechanics  their 
writings  were  a  sealed  book  to  every  one  on  this  side 
of  the  Atlantic,  and  so  remained  until  Bowditch  ap- 
peared, early  in  the  present  century.  His  transla- 
tion of  the  Mecanique  Celeste  made  an  epoch  in 
American  science  by  bringing  the  great  work  of  La- 
place down  to  the  reach  of  the  best  American  students 
of  his  time. 

American  astronomers  must  always  honor  the 
names  of  Rittenhouse  and  Bowditch.  And  yet  in 
one  respect  their  work  was  disappointing  of  results. 
Neither  of  them  was  the  founder  of  a  school.  Ritten- 
house left  no  successor  to  carry  on  his  work.  The 
help  which  Bowditch  afforded  his  generation  was 
invaluable  to  isolated  students  who,  here  and  there, 
dived  alone  and  unaided  into  the  mysteries  of  the 
celestial  motions.  His  work  was  not  mainly  in  the 
field  of  observational  astronomy,  and  therefore  did 
not  materially  influence  that  branch  of  science.  In 
1832  Professor  Airy,  afterwards  Astronomer  Royal  of 
England,  made  a  report  to  the  British  Association 
on  the  condition  of  practical  astronomy  in  various 
countries.  In  this  report  he  remarked  that  he  was 
unable  to  say  anything  about  American  astronomy 
because,  so  far  as  he  knew,  no  public  observatory 
existed  in  the  United  States. 

282 


ASPECTS    OF    AMERICAN    ASTRONOMY 

William  C.  Bond,  afterwards  famous  as  the  first 
director  of  the  Harvard  Observatory,  was  at  that 
time  making  observations  with  a  small  telescope, 
first  near  Boston  and  afterwards  at  Cambridge.  But 
with  so  meagre  an  outfit  his  establishment  could 
scarcely  lay  claim  to  being  an  astronomical  observa- 
tory, and  it  was  not  surprising  if  Airy  did  not  know 
anything  of  his  modest  efforts. 

If  at  this  time  Professor  Airy  had  extended  his  in- 
vestigations into  yet  another  field,  with  a  view  of 
determining  the  prospects  for  a  great  city  at  the 
site  of  Fort  Dearborn,  on  the  southern  shore  of  Lake 
Michigan,  he  would  have  seen  as  little  prospect  of 
civic  growth  in  that  region  as  of  a  great  development 
of  astronomy  in  the  United  States  at  large.  A  plat 
of  the  proposed  town  of  Chicago  had  been  prepared 
two  years  before,  when  the  place  contained  perhaps 
half  a  dozen  families.  In  the  same  month  in  which 
Professor  Airy  made  his  report,  August,  1832,  the 
people  of  the  place,  then  numbering  twenty-eight 
voters,  decided  to  become  incorporated,  and  selected 
five  trustees  to  carry  on  their  government. 

In  1837  a  city  charter  was  obtained  from  the  leg- 
islature of  Illinois.  The  growth  of  this  infant  city, 
then  small  even  for  an  infant,  into  the  great  com- 
mercial metropolis  of  the  West  has  been  the  just 
pride  of  its  people  and  the  wonder  of  the  world.  I 
mention  it  now  because  of  a  remarkable  coincidence. 
With  this  civic  growth  has  quietly  gone  on  another, 
little  noted  by  the  great  world,  and  yet  in  its  way 
equally  wonderful  and  equally  gratifying  to  the 
pride  of  those  who  measure  greatness  by  intellectual 
progress.  Taking  knowledge  of  the  universe  as  a 
measure  of  progress,  I  wish  to  invite  attention  to 

283 


SIDE-LIGHTS    ON    ASTRONOMY 

the  fact  that  American  astronomy  began  with  your 
city,  and  has  slowly  but  surely  kept  pace  with  it, 
until  to-day  our  country  stands  second  only  to  Ger- 
many in  the  number  of  researches  being  prosecuted, 
and  second  to  none  in  the  number  of  men  who  have 
gained  the  highest  recognition  by  their  labors. 

In  1836  Professor  Albert  Hopkins,  of  Williams 
College,  and  Professor  Elias  Loomis,  of  Western  Re- 
serve College,  Ohio,  both  commenced  little  observa- 
tories. Professor  Loomis  went  to  Europe  for  all 
his  instruments,  but  Hopkins  was  able  even  then  to 
get  some  of  his  in  this  country.  Shortly  afterwards 
a  little  wooden  structure  was  erected  by  Captain 
Gilliss  on  Capitol  Hill,  at  Washington,  and  supplied 
with  a  transit  instrument  for  observing  moon  cul- 
minations, in  conjunction  with  Captain  Wilkes,  who 
was  then  setting  out  on  his  exploring  expedition  to 
the  southern  hemisphere.  The  date  of  these  observ- 
atories was  practically  the  same  as  that  on  which 
a  charter  for  the  city  of  Chicago  was  obtained  from 
the  legislature.  With  their  establishment  the  popu- 
lation of  your  city  had  increased  to  703. 

The  next  decade,  1840  to  1850,  was  that  in  which 
our  practical  astronomy  seriously  commenced.  The 
little  observatory  of  Captain  Gilliss  was  replaced  by 
the  Naval,  then  called  the  National  Observatory, 
erected  at  Washington  during  the  years  1843-44,  and 
fitted  out  with  what  were  then  the  most  approved 
instruments.  About  the  same  time  the  appearance 
of  the  great  comet  of  1843  led  the  citizens  of  Boston 
to  erect  the  observatory  of  Harvard  College.  Thus 
it  is  little  more  than  a  half-century  since  the  two 
principal  observatories  in  the  United  States  were  es- 
tablished. But  we  must  not  for  a  moment  suppose 

284 


ASPECTS    OF   AMERICAN    ASTRONOMY 

that  the  mere  erection  of  an  observatory  can  mark 
an  epoch  in  scientific  history.  What  must  make  the 
decade  of  which  I  speak  ever  memorable  in  Ameri- 
can astronomy  was  not  merely  the  erection  of  build- 
ings, but  the  character  of  the  work  done  by  astron- 
omers away  from  them  as  well  as  in  them. 

The  National  Observatory  soon  became  famous 
by  two  remarkable  steps  which  raised  our  country 
to  an  important  position  among  those  applying 
modern  science  to  practical  uses.  One  of  these  con- 
sisted of  the  researches  of  Sears  Cook  Walker  on  the 
motion  of  the  newly  discovered  planet  Neptune. 
He  was  the  first  astronomer  to  determine  fairly  good 
elements  of  the  orbit  of  that  planet,  and,  what  is  yet 
more  remarkable,  he  was  able  to  trace  back  the 
movement  of  the  planet  in  the  heavens  for  half  a 
century  and  to  show  that  it  had  been  observed  as  a 
fixed  star  by  Lalande  in  1795,  without  the  observer 
having  any  suspicion  of  the  true  character  of  the 
object. 

The  other  work  to  which  I  refer  was  the  application 
to  astronomy  and  to  the  determination  of  longitudes 
of  the  chronographic  method  of  registering  transits 
of  stars  or  other  phenomena  requiring  an  exact  rec- 
ord of  the  instant  of  their  occurrence.  It  is  to  be 
regretted  that  the  history  of  this  application  has  not 
been  fully  written.  In  some  points  there  seems  to 
be  as  much  obscurity  as  with  the  discovery  of  ether 
as  an  anaesthetic,  which  took  place  about  the  same 
time.  Happily,  no  such  contest  has  been  fought 
over  the  astronomical  as  over  the  surgical  discovery, 
the  fact  being  that  all  who  were  engaged  in  the  ap- 
plication of  the  new  method  were  more  anxious  to 
perfect  it  than  they  were  to  get  credit  for  themselves. 

285 


SIDE-LIGHTS    ON    ASTRONOMY 

We  know  that  Saxton,  of  the  Coast  Survey ;  Mitchell 
and  Locke,  of  Cincinnati;  Bond,  at  Cambridge,  as 
well  as  Walker,  and  other  astronomers  at  the  Naval 
Observatory,  all  worked  at  the  apparatus;  that 
Maury  seconded  their  efforts  with  untiring  zeal ;  that 
it  was  used  to  determine  the  longitude  of  Baltimore 
as  early  as  1844  by  Captain  Wilkes,  and  that  it  was 
put  into  practical  use  in  recording  observations  at 
the  Naval  Observatory  as  early  as  1846. 

At  the  Cambridge  Observatory  the  two  Bonds, 
father  and  son,  speedily  began  to  show  the  stuff  of 
which  the  astronomer  is  made.  A  well-devised  sys- 
tem of  observations  was  put  in  operation.  The  dis- 
covery of  the  dark  ring  of  Saturn  and  of  a  new 
satellite  to  that  planet  gave  additional  fame  to  the 
establishment. 

Nor  was  activity  confined  to  the  observational  side 
of  the  science.  The  same  decade  of  which  I  speak 
was  marked  by  the  beginning  of  Professor  Pierce 's 
mathematical  work,  especially  his  determination  of 
the  perturbations  of  Uranus  and  Neptune.  At  this 
time  commenced  the  work  of  Dr.  B.  A.  Gould,  who 
soon  became  the  leading  figure  in  American  astron- 
omy. Immediately  on  graduating  at  Harvard  in 
1845,  he  determined  to  devote  all  the  energies  of  his 
life  to  the  prosecution  of  his  favorite  science.  He 
studied  in  Europe  for  three  years,  took  the  doctor's 
degree  at  Gottingen,  came  home,  founded  the  As- 
tronomical Journal,  and  took  an  active  part  in  that 
branch  of  the  work  of  the  Coast  Survey  which  in- 
cluded the  determination  of  longitudes  by  astronom- 
ical methods. 

An  episode  which  may  not  belong  to  the  history  of 
astronomy  must  be  acknowledged  to  have  had  a 

286 


ASPECTS    OF    AMERICAN    ASTRONOMY 

powerful  influence  in  exciting  public  interest  in  that 
science.  Professor  O.  M.  Mitchell,  the  founder  and 
first  director  of  the  Cincinnati  Observatory,  made 
the  masses  of  our  intelligent  people  acquainted  with 
the  leading  facts  of  astronomy  by  courses  of  lectures 
which,  in  lucidity  and  eloquence,  have  never  been 
excelled.  The  immediate  object  of  the  lectures  was 
to  raise  funds  for  establishing  his  observatory  and 
fitting  it  out  with  a  fine  telescope.  The  popular  in- 
terest thus  excited  in  the  science  had  an  important 
effect  in  leading  the  public  to  support  astronomical 
research.  If  public  support,  based  on  public  interest, 
is  what  has  made  the  present  fabric  of  American  as- 
tronomy possible,  then  should  we  honor  the  name  of 
a  man  whose  enthusiasm  leavened  the  masses  of  his 
countrymen  with  interest  in  our  science. 

The  Civil  War  naturally  exerted  a  depressing  in- 
fluence upon  our  scientific  activity.  The  cultivator 
of  knowledge  is  no  less  patriotic  than  his  fellow-citi- 
zens, and  vies  with  them  in  devotion  to  the  public 
welfare.  The  active  interest  which  such  cultivators 
took,  first  in  the  prosecution  of  the  war  and  then  in 
the  restoration  of  the  Union,  naturally  distracted 
their  attention  from  their  favorite  pursuits.  But  no 
sooner  was  political  stability  reached  than  a  wave  of 
intellectual  activity  set  in,  which  has  gone  on  increas- 
ing up  to  the  present  time.  If  it  be  true  that  never 
before  in  our  history  has  so  much  attention  been 
given  to  education  as  now ;  that  never  before  did  so 
many  men  devote  themselves  to  the  diffusion  of 
knowledge,  it  is  no  less  true  that  never  was  astro- 
nomical work  so  energetically  pursued  among  us  as 
at  the  present  time. 

One  deplorable  result  of  the  Civil  War  was  that 

287 


SIDE-LIGHTS    ON    ASTRONOMY 

Gould's  Astronomical  Journal  had  to  be  suspended. 
Shortly  after  the  restoration  of  peace,  instead  of  re- 
establishing the  journal,  its  founder  conceived  the 
project  of  exploring  the  southern  heavens.  The 
northern  hemisphere  being  the  seat  of  civilization, 
that  portion  of  the  sky  which  could  not  be  seen  from 
our  latitudes  was  comparatively  neglected.  What 
had  been  done  in  the  southern  hemisphere  was  most- 
ly the  occasional  work  of  individuals  and  of  one  or 
two  permanent  observatories.  The  latter  were  so 
few  in  number  and  so  meagre  in  their  outfit  that  a 
splendid  field  was  open  to  the  inquirer.  Gould  found 
the  patron  which  he  desired  in  the  government  of  the 
Argentine  Republic,  on  whose  territory  he  erected 
what  must  rank  in  the  future  as  one  of  the  memor- 
able astronomical  establishments  of  the  world.  His 
work  affords  a  most  striking  example  of  the  principle 
that  the  astronomer  is  more  important  than  his  in- 
struments. Not  only  were  the  means  at  the  com- 
mand of  the  Argentine  Observatory  slender  in  the 
extreme  when  compared  with  those  of  the  favored 
institutions  of  the  North,  but,  from  the  very  nature 
of  the  case,  the  Argentine  Republic  could  not  sup- 
ply trained  astronomers.  The  difficulties  thus  grow- 
ing out  of  the  administration  cannot  be  overesti- 
mated. And  yet  the  sixteen  great  volumes  in  which 
the  work  of  the  institution  has  been  published  will 
rank  in  the  future  among  the  classics  of  astronomy. 
Another  wonderful  focus  of  activity,  in  which  one 
hardly  knows  whether  he  ought  most  to  admire  the 
exhaustless  energy  or  the  admirable  ingenuity  which 
he  finds  displayed,  is  the  Harvard  Observatory.  Its 
work  has  been  aided  by  gifts  which  have  no  parallel 
in  the  liberality  that  prompted  them.  Yet  without 

288 


ASPECTS    OF    AMERICAN    ASTRONOMY 

energy  and  skill  such  gifts  would  have  been  useless. 
The  activity  of  the  establishment  includes  both 
hemispheres.  Time  would  fail  to  tell  how  it  has  not 
only  mapped  out  important  regions  of  the  heavens 
from  the  north  to  the  south  pole,  but  analyzed  the 
rays  of  light  which  come  from  hundreds  of  thousands 
of  stars  by  recording  their  spectra  in  permanence  on 
photographic  plates. 

The  work  of  the  establishment  is  so  organized  that 
a  new  star  cannot  appear  in  any  part  of  the  heavens 
nor  a  known  star  undergo  any  noteworthy  change 
without  immediate  detection  by  the  photographic 
eye  of  one  or  more  little  telescopes,  all-seeing  and 
never-sleeping  policemen  that  scan  the  heavens  un- 
ceasingly while  the  astronomer  may  sleep,  and  report 
in  the  morning  every  case  of  irregularity  in  the  pro- 
ceedings of  the  heavenly  bodies. 

Yet  another  example,  showing  what  great  results 
may  be  obtained  with  limited  means,  is  afforded  by 
the  Lick  Observatory,  on  Mount  Hamilton,  Cali- 
fornia. During  the  ten  years  of  its  activity  its  as- 
tronomers have  made  it  known  the  world  over  by 
works  and  discoveries  too  varied  and  numerous  to 
be  even  mentioned  at  the  present  time. 

The  astronomical  work  of  which  I  have  thus  far 
spoken  has  been  almost  entirely  that  done  at  ob- 
servatories. I  fear  that  I  may  in  this  way  have 
strengthened  an  erroneous  impression  that  the  seat 
of  important  astronomical  work  is  necessarily  con- 
nected with  an  observatory.  It  must  be  admitted 
that  an  institution  which  has  a  local  habitation  and 
a  magnificent  building  commands  public  attention 
so  strongly  that  valuable  work  done  elsewhere  may 
be  overlooked.  A  very  important  part  of  astronomi- 

289 


SIDE-LIGHTS    ON    ASTRONOMY 

cal  work  is  done  away  from  telescopes  and  meridian 
circles  and  requires  nothing  but  a  good  library  for 
its  prosecution.  One  who  is  devoted  to  this  side  of 
the  subject  may  often  feel  that  the  public  does  not 
appreciate  his  work  at  its  true  relative  value  from 
the  very  fact  that  he  has  no  great  buildings  or  fine 
instruments  to  show.  I  may  therefore  be  allowed 
to  claim  as  an  important  factor  in  the  American  as- 
tronomy of  the  last  half -century  an  institution  of 
which  few  have  heard  and  which  has  been  overlooked 
because  there  was  nothing  about  it  to  excite  at- 
tention. 

In  1849  the  American  Nautical  Almanac  office  was 
established  by  a  Congressional  appropriation.  The 
title  of  this  publication  is  somewhat  misleading  in 
suggesting  a  simple  enlargement  of  the  family  alma- 
nac which  the  sailor  is  to  hang  up  in  his  cabin  for 
daily  use.  The  fact  is  that  what  started  more  than 
a  century  ago  as  a  nautical  almanac  has  since  grown 
into  an  astronomical  ephemeris  for  the  publication  of 
everything  pertaining  to  times,  seasons,  eclipses,  and 
the  motions  of  the  heavenly  bodies.  It  is  the  work 
in  which  astronomical  observations  made  in  all  the 
great  observatories  of  the  world  are  ultimately 
utilized  for  scientific  and  public  purposes.  Each  of 
the  leading  nations  of  western  Europe  issues  such 
a  publication.  When  the  preparation  and  publica- 
tion of  the  American  ephemeris  was  decided  upon 
the  office  was  first  established  in  Cambridge,  the  seat 
of  Harvard  University,  because  there  could  most 
readily  be  secured  the  technical  knowledge  of  mathe- 
matics and  theoretical  astronomy  necessary  for  the 
work. 

A  field  of  activity  was  thus  opened,  of  which  a 

290 


ASPECTS    OF    AMERICAN    ASTRONOMY 

number  of  able  young  men  who  have  since  earned 
distinction  in  various  walks  of  life  availed  them- 
selves. The  head  of  the  office,  Commander  Davis, 
adopted  a  policy  well  fitted  to  promote  their  develop- 
ment. He  translated  the  classic  work  of  Gauss, 
Theoria  Motus  Corporum  Ccelestium,  and  made  the 
office  a  sort  of  informal  school,  not,  indeed,  of  the 
modern  type,  but  rather  more  like  the  classic  grove 
of  Hellas,  where  philosophers  conducted  their  dis- 
cussions and  profited  by  mutual  attrition.  When, 
after  a  few  years  of  experience,  methods  were  well 
established  and  a  routine  adopted,  the  office  was  re- 
moved to  Washington,  where  it  has  since  remained. 
The  work  of  preparing  the  ephemeris  has,  with  ex- 
perience, been  reduced  to  a  matter  of  routine  which 
may  be  continued  indefinitely,  with  occasional  changes 
in  methods  and  data,  and  improvements  to  meet  the 
increasing  wants  of  investigators. 

The  mere  preparation  of  the  ephemeris  includes 
but  a  small  part  of  the  work  of  mathematical  calcu- 
lation and  investigation  required  in  astronomy.  One 
of  the  great  wants  of  the  science  to-day  is  the  re- 
duction of  the  observations  made  during  the  first 
half  of  the  present  century,  and  even  during  the 
last  half  of  the  preceding  one.  The  labor  which  could 
profitably  be  devoted  to  this  work  would  be  more 
than  that  required  in  any  one  astronomical  observa- 
tory. It  is  unfortunate  for  this  work  that  a  great 
building  is  not  required  for  its  prosecution  because 
its  needfulness  is  thus  very  generally  overlooked  by 
that  portion  of  the  public  interested  in  the  progress 
of  science.  An  organization  especially  devoted  to 
it  is  one  of  the  scientific  needs  of  our  time. 

In  such  an  epoch-making  age  as  the  present  it  is 

291 


SIDE-LIGHTS    ON    ASTRONOMY 

dangerous  to  cite  any  one  step  as  making  a  new  epoch. 
Yet  it  may  be  that  when  the  historian  of  the  future 
reviews  the  science  of  our  day  he  will  find  the  most 
remarkable  feature  of  the  astronomy  of  the  last 
twenty  years  of  our  century  to  be  the  discovery  that 
this  steadfast  earth  of  which  the  poets  have  told  us 
is  not,  after  all,  quite  steadfast;  that  the  north  and 
south  poles  move  about  a  very  little,  describing 
curves  so  complicated  that  they  have  not  yet  been 
fully  marked  out.  The  periodic  variations  of  lati- 
tude thus  brought  about  were  first  suspected  about 
1880,  and  announced  with  some  modest  assurance  by 
Kustner,  of  Berlin,  a  few  years  later.  The  progress 
of  the  views  of  astronomical  opinion  from  incredulity 
to  confidence  was  extremely  slow  until,  about  1890, 
Chandler,  of  the  United  States,  by  an  exhaustive  dis- 
cussion of  innumerable  results  of  observations,  show- 
ed that  the  latitude  of  every  point  on  the  earth  was 
subject  to  a  double  oscillation,  one  having  a  period 
of  a  year,  the  other  of  four  hundred  and  twenty-seven 
days. 

Notwithstanding  the  remarkable  parallel  between 
the  growth  of  American  astronomy  and  that  of  your 
city,  one  cannot  but  fear  that  if  a  foreign  observer  had 
been  asked  only  half  a  dozen  years  ago  at  what  point 
in  the  United  States  a  great  school  of  theoretical  and 
practical  astronomy,  aided  by  an  establishment  for 
the  exploration  of  the  heavens,  was  likely  to  be  es- 
tablished by  the  munificence  of  private  citizens,  he 
would  have  been  wiser  than  most  foreigners  had  he 
guessed  Chicago.  Had  this  place  been  suggested  to 
him,  I  fear  he  would  have  replied  that  were  it  possible 
to  utilize  celestial  knowledge  in  acquiring  earthly 
wealth,  here  would  be  the  most  promising  seat  for 

292 


ASPECTS    OF    AMERICAN    ASTRONOMY 

such  a  school.  But  he  would  need  to  have  been  a 
little  wiser  than  his  generation  to  reflect  that  wealth 
is  at  the  base  of  all  progress  in  knowledge  and  the 
liberal  arts;  that  it  is  only  when  men  are  relieved 
from  the  necessity  of  devoting  all  their  energies  to 
the  immediate  wants  of  life  that  they  can  lead  the 
intellectual  life,  and  that  we  should  therefore  look  to 
the  most  enterprising  commercial  centre  as  the  like- 
liest seat  for  a  great  scientific  institution. 

Now  we  have  the  school,  and  we  have  the  observa- 
tory, which  we  hope  will  in  the  near  future  do  work 
that  will  cast  lustre  on  the  name  of  its  founder  as 
well  as  on  the  astronomers  who  may  be  associated 
with  it.  You  will,  I  am  sure,  pardon  me  if  I  make 
some  suggestions  on  the  subject  of  the  future  needs 
of  the  establishment.  We  want  this  newly  founded 
institution  to  be  a  great  success,  to  do  work  which 
shall  show  that  the  intellectual  productiveness  of  your 
community  will  not  be  allowed  to  lag  behind  its  ma- 
terial growth.  The  public  is  very  apt  to  feel  that 
when  some  munificent  patron  of  science  has  mounted 
a  great  telescope  under  a  suitable  dome,  and  supplied 
all  the  apparatus  which  the  astronomer  wants  to  use, 
success  is  assured.  But  such  is  not  the  case.  The 
most  important  requisite,  one  more  difficult  to  com- 
mand than  telescopes  or  observatories,  may  still  be 
wanting.  A  great  telescope  is  of  no  use  without  a 
man  at  the  end  of  it,  and  what  the  telescope  may  do 
depends  more  upon  this  appendage  than  upon  the  in- 
strument itself.  The  place  which  telescopes  and  ob- 
servatories have  taken  in  astronomical  history  are  by 
no  means  proportional  to  their  dimensions.  Many  a 
great  instrument  has  been  a  mere  toy  in  the  hands  of 
its  owner.  Many  a  small  one  has  become  famous. 

293 


SIDE-LIGHTS    ON    ASTRONOMY 

Twenty  years  ago  there  was  here  in  your  own  city 
a  modest  little  instrument  which,  judged  by  its  size, 
could  not  hold  up  its  head  with  the  great  ones  even 
of  that  day.  It  was  the  private  property  of  a  young 
man  holding  no  scientific  position  and  scarcely  known 
to  the  public.  And  yet  that  little  telescope  is  to-day 
among  the  famous  ones  of  the  world,  having  made 
memorable  advances  in  the  astronomy  of  double 
stars,  and  shown  its  owner  to  be  a  worthy  successor 
of  the  Herschels  and  Struves  in  that  line  of  work. 

A  hundred  observers  might  have  used  the  appli- 
ances of  the  Lick  Observatory  for  a  whole  generation 
without  finding  the  fifth  satellite  of  Jupiter;  without 
successfully  photographing  the  cloud  forms  of  the 
Milky  Way;  without  discovering  the  extraordinary 
patches  of  nebulous  light,  nearly  or  quite  invisible 
to  the  human  eye,  which  fill  some  regions  of  the 
heavens.  • 

When  I  was  in  Zurich  last  year  I  paid  a  visit  to  the 
little,  but  not  unknown,  observatory  of  its  famous 
polytechnic  school.  The  professor  of  astronomy  was 
especially  interested  in  the  observations  of  the  sun 
with  the  aid  of  the  spectroscope,  and  among  the  in- 
genious devices  which  he  described,  not  the  least 
interesting  was  the  method  of  photographing  the 
sun  by  special  rays  of  the  spectrum,  which  had  been 
worked  out  at  the  Kenwood  Observatory  in  Chicago. 
The  Kenwood  Observatory  is  not,  I  believe,  in  the 
eye  of  the  public,  one  of  the  noteworthy  institutions 
of  your  city  which  every  visitor  is  taken  to  see,  and 
yet  this  invention  has  given  it  an  important  place  in 
the  science  of  our  day. 

Should  you  ask  me  what  are  the  most  hopeful  feat- 
ures in  the  great  establishment  which  you  are  now 

294 


ASPECTS    OF    AMERICAN    ASTRONOMY 

dedicating,  I  would  say  that  they  are  not  alone  to 
be  found  in  the  size  of  your  unequalled  telescope,  nor 
in  the  cost  of  the  outfit,  but  in  the  fact  that  your 
authorities  have  shown  their  appreciation  of  the  re- 
quirements of  success  by  adding  to  the  material  out- 
fit of  the  establislunent  the  three  men  whose  works 
I  have  described. 

Gentlemen  of  the  trustees,  allow  me  to  commend 
to  your  fostering  care  the  men  at  the  end  of  the  tele- 
scope. The  constitution  of  the  astronomer  shows 
curious  and  interesting  features.  If  he  is  destined 
to  advance  the  science  by  works  of  real  genius,  he 
must,  like  the  poet,  be  born,  not  made.  The  born 
astronomer,  when  placed  in  command  of  a  telescope, 
goes  about  using  it  as  naturally  and  effectively  as  the 
babe  avails  itself  of  its  mother's  breast.  He  sees 
intuitively  what  less  gifted  men  have  to  learn  by 
long  study  and  tedious  experiment.  He  is  moved  to 
celestial  knowledge  by  a  passion  which  dominates 
his  nature.  He  can  no  more  avoid  doing  astronomical 
work,  whether  in  the  line  of  observations  or  research, 
than  a  poet  can  chain  his  Pegasus  to  earth.  I  do 
not  mean  by  this  that  education  and  training  will  be 
of  no  use  to  him.  They  will  certainly  accelerate  his 
early  progress.  If  he  is  to  become  great  on  the 
mathematical  side,  not  only  must  his  genius  have 
a  bend  in  that  direction,  but  he  must  have  the  means 
of  pursuing  his  studies.  And  yet  I  have  seen  so 
many  failures  of  men  who  had  the  best  instruction, 
and  so  many  successes  of  men  who  scarcely  learned 
anything  of  their  teachers,  that  I  sometimes  ask 
whether  the  great  American  celestial  mechanician 
of  the  twentieth  century  will  be  a  graduate  of  a  uni- 
versity or  of  the  backwoods, 
ao  295 


SIDE-LIGHTS    ON    ASTRONOMY 

Is  the  man  thus  moved  to  the  exploration  of  nature 
by  an  unconquerable  passion  more  to  be  envied  or 
pitied  ?  In  no  other  pursuit  does  success  come  with 
such  certainty  to  him  who  deserves  it.  No  life  is  so 
enjoyable  as  that  whose  energies  are  devoted  to  fol- 
lowing out  the  inborn  impulses  of  one's  nature.  The 
investigator  of  truth  is  little  subject  to  the  disap- 
pointments which  await  the  ambitious  man  in  other 
fields  of  activity.  It  is  pleasant  to  be  one  of  a  broth- 
erhood extending  over  the  world,  in  which  no  rivalry 
exists  except  that  which  comes  out  of  trying  to  do 
better  work  than  any  one  else,  while  mutual  admira- 
tion stifles  jealousy.  And  yet,  with  all  these  ad- 
vantages, the  experience  of  the  astronomer  may  have 
its  dark  side.  As  he  sees  his  field  widening  faster 
than  he  can  advance  he  is  impressed  with  the  little- 
ness of  all  that  can  be  done  in  one  short  life.  He 
feels  the  same  want  of  successors  to  pursue  his  work 
that  the  founder  of  a  dynasty  may  feel  for  heirs  to 
occupy  his  throne.  He  has  no  desire  to  figure  in 
history  as  a  Napoleon  of  science  whose  conquests 
must  terminate  with  his  life.  Even  during  his  active 
career  his  work  may  be  such  a  kind  as  to  require 
the  co-operation  of  others  and  the  active  support  of 
the  public.  If  he  is  disappointed  in  commanding 
these  requirements,  if  he  finds  neither  co-operation 
nor  support,  if  some  great  scheme  to  which  he  may 
have  devoted  much  of  his  life  thus  proves  to  be  only 
a  castle  in  the  air,  he  may  feel  that  nature  has  dealt 
hardly  with  him  in  not  endowing  him  with  passions 
like  to  those  of  other  men. 

In  treating  a  theme  of  perennial  interest  one  nat- 
urally tries  to  fancy  what  the  future  may  have  in 
store.  If  the  traveller,  contemplating  the  ruins  of 

296 


ASPECTS    OF    AMERICAN    ASTRONOMY 

some  ancient  city  which  in  the  long  ago  teemed  with 
the  life  and  activities  of  generations  of  men,  sees  every 
stone  instinct  with  emotion  and  the  dust  alive  with 
memories  of  the  past,  may  he  not  be  similarly  im- 
pressed when  he  feels  that  he  is  looking  around  upon 
a  seat  of  future  empire — a  region  where  generations 
yet  unborn  may  take  a  leading  part  in  moulding  the 
history  of  the  world?  What  may  we  not  expect  of 
that  energy  which  in  sixty  years  has  transformed  a 
straggling  village  into  one  of  the  world's  great  cen- 
tres of  commerce?  May  it  not  exercise  a  powerful 
influence  on  the  destiny  not  only  of  the  country 
but  of  the  world?  If  so,  shall  the  power  thus  to 
be  exercised  prove  an  agent  of  beneficence,  diffus- 
ing light  and  life  among  nations,  or  shall  it  be  the 
opposite  ? 

The  time  must  come  ere  long  when  wealth  shall 
outgrow  the  field  in  which  it  can  be  profitably  em- 
ployed. In  what  direction  shall  its  possessors  then 
look?  Shall  they  train  a  posterity  which  will  so  use 
its  power  as  to  make  the  world  better  that  it  has 
lived  in  it?  Will  the  future  heir  to  great  wealth 
prefer  the  intellectual  life  to  the  life  of  pleasure  ? 

We  can  have  no  more  hopeful  answer  to  these 
questions  than  the  establishment  of  this  great  uni- 
versity in  the  very  focus  of  the  commercial  activity 
of  the  West.  Its  connection  with  the  institution  we 
have  been  dedicating  suggests  some  thoughts  on 
science  as  a  factor  in  that  scheme  of  education  best 
adapted  to  make  the  power  of  a  wealthy  community 
a  benefit  to  the  race  at  large.  When  we  see  what  a 
factor  science  has  been  in  our  present  civilization, 
how  it  has  transformed  the  world  and  increased  the 
means  of  human  enjoyment  by  enabling  men  to 

297 


SIDE-LIGHTS    ON    ASTRONOMY 

apply  the  powers  of  nature  to  their  own  uses,  it  is 
not  wonderful  that  it  should  claim  the  place  in  edu- 
cation hitherto  held  by  classical  studies.  In  the  con- 
test which  has  thus  arisen  I  take  no  part  but  that 
of  a  peace-maker,  holding  that  it  is  as  important  to 
us  to  keep  in  touch  with  the  traditions  of  our  race, 
and  to  cherish  the  thoughts  which  have  come  down 
to  us  through  the  centuries,  as  it  is  to  enjoy  and  util- 
ize what  the  present  has  to  offer  us.  Speaking  from 
this  point  of  view,  I  would  point  out  the  error  of 
making  the  utilitarian  applications  of  knowledge  the 
main  object  in  its  pursuit.  It  is  an  historic  fact  that 
abstract  science — science  pursued  without  any  utili- 
tarian end — has  been  at  the  base  of  our  progress  in 
the  utilization  of  knowledge.  If  in  the  last  century 
such  men  as  Galvani  and  Volta  had  been  moved  by 
any  other  motive  than  love  of  penetrating  the  secrets 
of  nature  they  would  never  have  pursued  the  seem- 
ingly useless  experiments  they  did,  and  the  founda- 
tion of  electrical  science  would  not  have  been  laid. 
Our  present  applications  of  electricity  did  not  become 
possible  until  Ohm's  mathematical  laws  of  the  electric 
current,  which  when  first  made  known  seemed  little 
more  than  mathematical  curiosities,  had  become  the 
common  property  of  inventors.  Professional  pride 
on  the  part  of  our  own  Henry  led  him,  after  making 
the  discoveries  which  rendered  the  telegraph  possible, 
to  go  no  further  in  their  application,  and  to  live  and 
die  without  receiving  a  dollar  of  the  millions  which 
the  country  has  won  through  his  agency. 

In  the  spirit  of  scientific  progress  thus  shown  we 
have  patriotism  in  its  highest  form — a  sentiment 
which  does  not  seek  to  benefit  the  country  at  the  ex- 
pense of  the  world,  but  to  benefit  the  world  by  means 

298 


ASPECTS    OF    AMERICAN    ASTRONOMY 

of  one's  country.  Science  has  its  competition,  as 
keen  as  that  which  is  the  life  of  commerce.  But  its 
rivalries  are  over  the  question  who  shall  contribute 
the  most  and  the  best  to  the  sum  total  of  knowledge ; 
who  shall  give  the  most,  not  who  shall  take  the  most. 
Its  animating  spirit  is  love  of  truth.  Its  pride  is  to 
do  the  greatest  good  to  the  greatest  number.  It  em- 
braces not  only  the  whole  human  race  but  all  nature 
in  its  scope.  The  public  spirit  of  which  this  city  is 
the  focus  has  made  the  desert  blossom  as  the  rose, 
and  benefited  humanity  by  the  diffusion  of  the  ma- 
terial products  of  the  earth.  Should  you  ask  me  how 
it  is  in  the  future  to  use  its  influence  for  the  benefit 
of  humanity  at  large,  I  would  say,  look  at  the  work 
now  going  on  in  these  precincts,  and  study  its  spirit. 
Here  are  the  agencies  which  will  make  "the  voice 
of  law  the  harmony  of  the  world."  Here  is  the  love 
of  country  blended  with  love  of  the  race.  Here  the 
love  of  knowledge  is  as  unconfmed  as  your  commercial 
enterprise.  Let  not  your  youth  come  hither  merely 
to  learn  the  forms  of  vertebrates  and  the  properties 
of  oxides,  but  rather  to  imbibe  that  catholic  spirit 
which,  animating  their  growing  energies,  shall  make 
the  power  they  are  to  wield  an  agent  of  beneficence 
to  all  mankind. 


XIX 

THE    UNIVERSE    AS    AN    ORGANISM* 

IF  I  were  called  upon  to  convey,  within  the  com- 
pass of  a  single  sentence,  an  idea  of  the  trend  of 
recent  astronomical  and  physical  science,  I  should 
say  that  it  was  in  the  direction  of  showing  the  uni- 
verse to  be  a  connected  whole.  The  farther  we  ad- 
vance in  knowledge,  the  clearer  it  becomes  that  the 
bodies  which  are  scattered  through  the  celestial 
spaces  are  not  completely  independent  existences, 
but  have,  with  all  their  infinite  diversity,  many  at- 
tributes in  common. 

In  this  we  are  going  in  the  direction  of  certain  ideas 
of  the  ancients  which  modern  discovery  long  seemed 
to  have  contradicted.  In  the  infancy  of  the  race, 
the  idea  that  the  heavens  were  simply  an  enlarged 
and  diversified  earth,  peopled  by  beings  who  could 
roam  at  pleasure  from  one  extreme  to  the  other,  was 
a  quite  natural  one.  The  crystalline  sphere  or  spheres 
which  contained  all  formed  a  combination  of  ma- 
chinery revolving  on  a  single  plan.  But  all  bonds 
of  unity  between  the  stars  began  to  be  weakened 
when  Copernicus  showed  that  there  were  no  spheres, 
that  the  planets  were  isolated  bodies,  and  that  the 

*  Address  before  the  Astronomical  and  Astrophysical  Society  of 
America,  December  29,  1902. 

300 


THE    UNIVERSE    AS    AN    ORGANISM 

stars  were  vastly  more  distant  than  the  planets.  As 
discovery  went  on  and  our  conceptions  of  the  uni- 
verse were  enlarged,  it  was  found  that  the  system  of 
the  fixed  stars  was  made  up  of  bodies  so  vastly  dis- 
tant and  so  completely  isolated  that  it  was  difficult 
to  conceive  of  them  as  standing  in  any  definable  re- 
lation to  one  another.  It  is  true  that  they  all  emitted 
light,  else  we  could  not  see  them,  and  the  theory  of 
gravitation,  if  extended  to  such  distances,  a  fact  not 
then  proved,  showed  that  they  acted  on  one  another 
by  their  mutual  gravitation.  But  this  was  all. 
Leaving  out  light  and  gravitation,  the  universe  was 
still,  in  the  time  of  Herschel,  composed  of  bodies 
which,  for  the  most  part,  could  not  stand  in  any 
known  relation  one  to  the  other. 

When,  forty  years  ago,  the  spectroscope  was  ap- 
plied to  analyze  the  light  coming  from  the  stars,  a 
field  was  opened  not  less  .fruitful  than  that  which  the 
telescope  made  known  to  Galileo.  The  first  conclu- 
sion reached  was  that  the  sun  was  composed  almost 
entirely  of  the  same  elements  that  existed  upon  the 
earth.  Yet,  as  the  bodies  of  our  solar  system  were 
evidently  closely  related,  this  was  not  remarkable. 
But  very  soon  the  same  conclusion  was,  to  a  limited 
extent,  extended  to  the  fixed  stars  in  general.  Such 
elements  as  iron,  hydrogen,  and  calcium  were  found 
not  to  belong  merely  to  our  earth,  but  to  form  im- 
portant constituents  of  the  whole  universe.  We  can 
conceive  of  no  reason  why,  out  of  the  infinite  num- 
ber of  combinations  which  might  make  up  a  spec- 
trum, there  should  not  be  a  separate  kind  of  matter 
for  each  combination.  So  far  as  we  know,  the  ele- 
ments might  merge  into  one  another  by  insensible 
gradations.  It  is,  therefore,  a  remarkable  and  sug- 

301 


SIDE-LIGHTS    ON    ASTRONOMY 

gestive  fact  when  we  find  that  the  elements  which 
make  up  bodies  so  widely  separate  that  we  can  hardly 
imagine  them  having  anything  in  common,  should 
be  so  much  the  same. 

In  recent  times  what  we  may  regard  as  a  new 
branch  of  astronomical  science  is  being  developed, 
showing  a  tendency  towards  unity  of  structure 
throughout  the  whole  domain  of  the  stars.  This  is 
what  we  now  call  the  science  of  stellar  statistics. 
The  very  conception  of  such  a  science  might  almost 
appall  us  by  its  immensity.  The  widest  statistical 
field  in  other  branches  of  research  is  that  occupied 
by  sociology.  Every  country  has  its  census,  in  which 
the  individual  inhabitants  are  classified  on  the  largest 
scale  and  the  combination  of  these  statistics  for  dif- 
ferent countries  may  be  said  to  include  all  the  inter- 
est of  the  human  race  within  its  scope.  Yet  this 
field  is  necessarily  confined  to  the  surface  of  our 
planet.  In  the  field  of  stellar  statistics  millions  of 
stars  are  classified  as  if  each  taken  individually  were 
of  no  more  weight  in  the  scale  than  a  single  inhabi- 
tant of  China  in  the  scale  of  the  sociologist.  And  yet 
the  most  insignificant  of  these  suns  may,  for  aught 
we  know,  have  planets  revolving  around  it,  the  in- 
terests of  whose  inhabitants  cover  as  wide  a  range 
as  ours  do  upon  our  own  globe. 

The  statistics  of  the  stars  may  be  said  to  have 
commenced  with  Herschel's  gauges  of  the  heavens, 
which  were  continued  from  time  to  time  by  various 
observers,  never,  however,  on  the  largest  scale.  The 
subject  was  first  opened  out  into  an  illimitable  field 
of  research  through  a  paper  presented  by  Kapteyn 
to  the  Amsterdam  Academy  of  Sciences  in  1893. 
The  capital  results  of  this  paper  were  that  different 

302 


THE    UNIVERSE    AS    AN    ORGANISM 

regions  of  space  contain  different  kinds  of  stars  and, 
more  especially,  that  the  stars  of  the  Milky  Way  be- 
long, in  part  at  least,  to  a  different  class  from  those 
existing  elsewhere.  Stars  not  belonging  to  the  Milky 
Way  are,  in  large  part,  of  a  distinctly  different  class. 

The  outcome  of  Kapteyn's  conclusions  is  that  we 
are  able  to  describe  the  universe  as  a  single  object, 
with  some  characters  of  an  organized  whole.  A 
large  part  of  the  stars  which  compose  it  may  be 
considered  as  divisible  into  two  groups.  One  of 
these  comprises  the  stars  composing  the  great  girdle 
of  the  Milky  Way.  These  are  distinguished  from 
the  others  by  being  bluer  in  color,  generally  greater 
in  absolute  brilliancy,  and  affected,  there  is  some 
reason  to  believe,  with  rather  slower  proper  motions. 
The  other  classes  are  stars  with  a  greater  or  less 
shade  of  yellow  in  their  color,  scattered  through  a 
spherical  space  of  unknown  dimensions,  but  con- 
centric with  the  Milky  Way.  Thus  a  sphere  with 
a  girdle  passing  around  it  forms  the  nearest  ap- 
proach to  a  conception  of  the  universe  which  we  can 
reach  to-day.  The  number  of  stars  in  the  girdle  is 
much  greater  than  that  in  the  sphere. 

The  feature  of  the  universe  which  should  therefore 
command  our  attention  is  the  arrangement  of  a  large 
part  of  the  stars  which  compose  it  in  a  ring,  seemingly 
alike  in  all  its  parts,  so  far  as  general  features  are  con- 
cerned. So  far  as  research  has  yet  gone,  we  are  not 
able  to  say  decisively  that  one  region  of  this  ring 
differs  essentially  from  another.  It  may,  therefore, 
be  regarded  as  forming  a  structure  built  on  a  uniform 
plan  throughout. 

All  scientific  conclusions  drawn  from  statistical 
data  require  a  critical  investigation  of  the  basis  on 

303 


SIDE-LIGHTS    ON    ASTRONOMY 

which  they  rest.  If  we  are  going,  from  merely  count- 
ing the  stars,  observing  their  magnitudes  and  deter- 
mining their  proper  motions,  to  draw  conclusions  as  to 
the  structure  of  the  universe  in  space,  the  question 
may  arise  how  we  can  form  any  estimate  whatever 
of  the  possible  distance  of  the  stars,  a  conclusion  as 
to  which  must  be  the  very  first  step  we  take.  We 
can  hardly  say  that  the  parallaxes  of  more  than  one 
hundred  stars  have  been  measured  with  any  approach 
to  certainty.  The  individuals  of  this  one  hundred  are 
situated  at  very  different  distances  from  us.  We 
hope,  by  long  and  repeated  observations,  to  make  a 
fairly  approximate  determination  of  the  parallaxes 
of  all  the  stars  whose  distance  is  less  than  twenty  times 
that  of  a  Centauri.  But  how  can  we  know  anything 
about  the  distance  of  stars  outside  this  sphere? 
What  can  we  say  against  the  view  of  Kepler  that  the 
space  around  our  sun  is  very  much  thinner  in  stars 
than  it  is  at  a  greater  distance ;  in  fact,  that,  the  great 
mass  of  the  stars  may  be  situated  between  the  sur- 
faces of  two  concentrated  spheres  not  very  different 
in  radius.  May  not  this  universe  of  stars  be  some- 
what in  the  nature  of  a  hollow  sphere  ? 

This  objection  requires  very  careful  consideration 
on  the  part  of  all  who  draw  conclusions  as  to  the  dis- 
tribution of  stars  in  space  and  as  to  the  extent  of  the 
visible  universe.  The  steps  to  a  conclusion  on  the 
subject  are  briefly  these:  First,  we  have  a  general  con- 
clusion, the  basis  of  which  I  have  already  set  forth, 
that,  to  use  a  loose  expression,  there  are  likenesses 
throughout  the  whole  diameter  of  the  universe.  There 
is,  therefore,  no  reason  to  suppose  that  the  region  in 
which  our  system  is  situated  differs  in  any  essential 
degree  from  any  other  region  near  the  central  portion. 

304 


THE    UNIVERSE    AS    AN    ORGANISM 

» 

Again,  spectroscopic  examinations  seem  to  show  that 
all  the  stars  are  in  motion,  and  that  we  cannot  say 
that  those  in  one  part  of  the  universe  move  more 
rapidly  than  those  in  another.  This  result  is  of  the 
greatest  value  for  our  purpose,  because,  when  we 
consider  only  the  apparent  motions,  as  ordinarily 
observed,  these  are  necessarily  dependent  upon  the 
distance  of  the  star.  We  cannot,  therefore,  infer  the 
actual  speed  of  a  star  from  ordinary  observations  un- 
til we  know  its  distance.  But  the  results  of  spectro- 
scopic measurements  of  radial  velocity  are  indepen- 
dent of  the  distance  of  the  star. 

But  let  us  not  claim  too  much.  We  cannot  yet 
say  with  certainty  that  the  stars  which  form  the 
agglomerations  of  the  Milky  Way  have,  beyond  doubt, 
the  same  average  motion  as  the  stars  in  other  regions 
of  the  universe.  The  difficulty  is  that  these  stars  ap- 
pear to  us  so  faint  individually,  that  the  investigation 
of  their  spectra  is  still  beyond  the  powers  of  our  in- 
struments. But  the  extraordinary  feat  performed  at 
the  Lick  Observatory  of  measuring  the  radial  motion 
of  1830  Groombridge,  a  star  quite  invisible  to  the 
naked  eye,  and  showing  that  it  is  approaching  our 
system  with  a  speed  of  between  fifty  and  sixty  miles 
a  second,  may  lead  us  to  hope  for  a  speedy  solution 
of  this  question.  But  we  need  not  await  this  result 
in  order  to  reach  very  probable  conclusions.  The 
general  outcome  of  researches  on  proper  motions 
tends  to  strengthen  the  conclusions  that  the  Keplerian 
sphere,  if  I  may  use  this  expression,  has  no  very  well 
marked  existence.  The  laws  of  stellar  velocity  and 
the  statistics  of  proper  motions,  while  giving  some 
color  to  the  view  that  the  space  in  which  we  are  sit- 
uated is  thinner  in  stars  than  elsewhere,  yet  show  that, 


SIDE-LIGHTS    ON    ASTRONOMY 

as  a  general  rule,  there  are  no  great  agglomerations  of 
stars  elsewhere  than  in  the  region  of  the  Milky  Way. 

With  unity  there  is  always  diversity;  in  fact,  the 
unity  of  the  universe  on  which  I  have  been  insisting 
consists  in  part  of  diversity.  It  is  very  curious  that, 
among  the  many  thousands  of  stars  which  have  been 
spectroscopically  examined,  no  two  are  known  to 
have  absolutely  the  same  physical  constitution.  It 
is  true  that  there  are  a  great  many  resemblances. 
a  Centauri,  our  nearest  neighbor,  if  we  can  use  such  a 
word  as  "near"  in  speaking  of  its  distance,  has  a 
spectrum  very  like  that  of  our  sun,  and  so  has  Capella. 
But  even  in  these  cases  careful  examination  shows 
differences.  These  differences  arise  from  variety  in 
the  combinations  and  temperature  of  the  substances 
of  which  the  star  is  made  up.  Quite  likely  also,  ele- 
ments not  known  on  the  earth  may  exist  on  the  stars, 
but  this  is  a  point  on  which  we  cannot  yet  speak  with 
certainty. 

Perhaps  the  attribute  in  which  the  stars  show  the 
greatest  variety  is  that  of  absolute  luminosity.  One 
hundred  years  ago  it  was  naturally  supposed  that 
the  brighter  stars  were  the  nearest  to  us,  and  this  is 
doubtless  true  when  we  take  the  general  average. 
But  it  was  soon  found  that  we  cannot  conclude  that 
because  a  star  is  bright,  therefore  it  is  near.  The 
most  striking  example  of  this  is  afforded  by  the 
absence  of  measurable  parallaxes  in  the  two  bright 
stars,  Canopus  and  Rigel,  showing  that  these  stars, 
though  of  the  first  magnitude,  are  immeasurably 
distant.  A  remarkable  fact  is  that  these  conclusions 
coincide  with  that  which  we  draw  from  the  minute- 
ness of  the  proper  motions.  Rigel  has  no  motion 
that  has  certainly  been  shown  by  more  than  a  cen- 

306 


STAR    SPECTRA 


THE    UNIVERSE    AS    AN    ORGANISM 

tury  of  observation,  and  it  is  not  certain  that  Canopus 
has  either.  From  this  alone  we  may  conclude,  with 
a  high  degree  of  probability,  that  the  distance  of  each 
is  immeasurably  great.  We  may  say  with  certainty 
that  the  brightness  of  each  is  thousands  of  times  that 
of  the  sun,  and  with  a  high  degree  of  probability  that 
it  is  hundreds  of  thousands  of  times.  On  the  other 
hand,  there  are  stars  comparatively  near  us  of  which 
the  light  is  not  the  hundredth  part  of  the  sun. 

The  universe  may  be  a  unit  in  two  ways.  One  is 
that  unity  of  structure  to  which  our  attention  has 
just  been  directed.  This  might  subsist  forever  with- 
out one  body  influencing  another.  The  other  form 
of  unity  leads  us  to  view  the  universe  as  an  organism. 
It  is  such  by  mutual  action  going  on  between  its 
bodies.  A  few  years  ago  we  could  hardly  suppose 
or  imagine  that  any  other  agents  than  gravitation 
and  light  could  possibly  pass  through  spaces  so  im- 
mense as  those  which  separate  the  stars. 

The  most  Remarkable  and  hopeful  characteristic 
of  the  unity  of  the  universe  is  the  evidence  which  is 
being  gathered  that  there  are  other  agencies  whose 
exact  nature  is  yet  unknown  to  us,  but  which  do 
pass  from  one  heavenly  body  to  another.  The  best 
established  example  of  this  yet  obtained  is  afforded 
in  the  case  of  the  sun  and  the  earth. 

The  fact  that  the  frequency  of  magnetic  storms 
goes  through  a  period  of  about  eleven  years,  and  is 
proportional  to  the  frequency  of  sun-spots,  has  been 
well  established.  The  recent  work  of  Professor  Bige- 
low  shows  the  coincidence  to  be  of  remarkable  exact- 
ness, the  curves  of  the  two  phenomena  being  prac- 
tically coincident  so  far  as  their  general  features  are 
concerned.  The  conclusion  is  that  spots  on  the  sun 

307 


SIDE-LIGHTS    ON    ASTRONOMY 

and  magnetic  storms  are  due  to  the  same  cause.  This 
cause  cannot  be  any  change  in  the  ordinary  radiation 
of  the  sun,  because  the  best  records  of  temperature 
show  that,  to  whatever  variations  the  sun's  radiation 
may  be  subjected,  they  do  not  change  in  the  period 
of  the  sun-spots.  To  appreciate  the  relation,  we  must 
recall  that  the  researches  of  Hale  with  the  spectro- 
heliograph  show  that  spots  are  not  the  primary 
phenomenon  of  solar  activity,  but  are  simply  the 
outcome  of  processes  going  on  constantly  in  the  sun 
which  result  in  spots  only  in  special  regions  and  on 
special  occasions.  It  does  not,  therefore,  necessarily 
follow  that  a  spot  does  cause  a  magnetic  storm.  What 
we  should  conclude  is  that  the  solar  activity  which 
produces  a  spot  also  produces  the  magnetic  storm. 

When  we  inquire  into  the  possible  nature  of  these 
relations  between  solar  activity  and  terrestrial  mag- 
netism, we  find  ourselves  so  completely  in  the  dark 
that  the  question  of  what  is  really  proved  by  the 
coincidence  may  arise.  Perhaps  the  most  obvious 
explanation  of  fluctuations  in  the  earth's  magnetic 
field  to  be  inquired  into  would  be  based  on  the  hy- 
pothesis that  the  space  through  which  the  earth  is 
moving  is  in  itself  a  varying  magnetic  field  of  vast 
extent.  This  explanation  is  tested  by  inquiring 
whether  the  fluctuations  in  question  can  be  explained 
by  supposing  a  disturbing  force  which  acts  substan- 
tially in  the  same  direction  all  over  the  globe.  But 
a  very  obvious  test  shows  that  this  explanation  is 
untenable.  Were  it  the  correct  one,  the  intensity 
of  the  force  in  some  regions  of  the  earth  would  be 
diminished  and  in  regions  where  the  needle  pointed 
in  the  opposite  direction  would  be  increased  in  exact- 
ly the  same  degree.  But  there  is  no  relation  traceable 

308 


THE    UNIVERSE    AS    AN    ORGANISM 

either  in  any  of  the  regular  fluctuations  of  the  mag- 
netic force,  or  in  those  irregular  ones  which  occur 
during  a  magnetic  storm.  If  the  horizontal  force  is 
increased  in  one  part  of  the  earth,  it  is  very  apt 
to  show  a  simultaneous  increase  the  world  over,  re- 
gardless of  the  direction  in  which  the  needle  may 
point  in  various  localities.  It  is  hardly  necessary  to 
add  that  none  of  the  fluctuations  in  terrestrial  mag- 
netism can  be  explained  on  the  hypothesis  that  either 
the  moon  or  the  sun  acts  as  a  magnet.  In  such  a 
case  the  action  would  be  substantially  in  the  same 
direction  at  the  same  moment  the  world  over. 

Such  being  the  case,  the  question  may  arise  whether 
the  action  producing  a  magnetic  storm  comes  from 
the  sun  at  all,  and  whether  the  fluctuations  in  the 
sun's  activity,  and  in  the  earth's  magnetic  field  may 
not  be  due  to  some  cause  external  to  both.  All  we 
can  say  in  reply  to  this  is  that  every  effort  to  find 
such  a  cause  has  failed  and  that  it  is  hardly  possible 
to  imagine  any  cause  producing  such  an  effect.  It  is 
true  that  the  solar  spots  were,  not  many  years  ago, 
supposed  to  be  due  in  some  way  to  the  action  of  the 
planets.  But,  for  reasons  which  it  would  be  tedious 
to  go  into  at  present,  we  may  fairly  regard  this 
hypothesis  as  being  completely  disproved.  There 
can,  I  conclude,  be  little  doubt  that  the  eleven-year 
cycle  of  change  in  the  solar  spots  is  due  to  a  cycle 
going  on  in  the  sun  itself.  Such  being  the  case,  the 
corresponding  change  in  the  earth's  magnetism  must 
be  due  to  the  same  cause. 

We  may,  therefore,  regard  it  as  a  fact  sufficiently 
established  to  merit  further  investigation  that  there 
does  emanate  from  the  sun,  in  an  irregular  way,  some 
agency  adequate  to  produce  a  measurable  effect  on 

309 


SIDE-LIGHTS    ON    ASTRONOMY 

the  magnetic  needle.  We  must  regard  it  as  a  singular 
fact  that  no  observations  yet  made  give  us  the  slight- 
est indication  as  to  what  this  emanation  is.  The  pos- 
sibility of  defining  it  is  suggested  by  the  discovery 
within  the  past  few  years,  that  under  certain  condi- 
tions, heated  matter  sends  forth  entities  known  as 
Rontgen  rays,  Becquerel  corpuscles  and  electrons. 
I  cannot  speak  authoritatively  on  this  subject,  but, 
so  far  as  I  am  aware,  no  direct  evidence  has  yet  been 
gathered  showing  that  any  of  these  entities  reach  us 
from  the  sun.  We  must  regard  the  search  for  the 
unknown  agency  so  fully  proved  as  among  the  most 
important  tasks  of  the  astronomical  physicist  of  the 
present  time.  From  what  we  know  of  the  history 
of  scientific  discovery,  it  seems  highly  probable  that, 
in  the  course  of  his  search,  he  will,  before  he  finds 
the  object  he  is  aiming  at,  discover  many  other  things 
of  equal  or  greater  importance  of  which  he  had,  at 
the  outset,  no  conception. 

The  main  point  I  desire  to  bring  out  in  this  review 
is  the  tendency  which  it  shows  towards  unification 
in  physical  research.  Heretofore  differentiation — the 
subdivision  of  workers  into  a  continually  increasing 
number  of  groups  of  specialists — has  been  the  rule. 
Now  we  see  a  coming  together  of  what,  at  first  sight, 
seem  the  most  widely  separated  spheres  of  activity. 
What  two  branches  could  be  more  widely  separated 
than  that  of  stellar  statistics,  embracing  the  whole 
universe  within  its  scope,  and  the  study  of  these 
newly  discovered  emanations,  the  product  of  our 
laboratories,  which  seem  to  show  the  existence  of 
corpuscles  smaller  than  the  atoms  of  matter?  And 
yet,  the  phenomena  which  we  have  reviewed,  especial- 
ly the  relation  of  terrestrial  magnetism  to  the  solar 

310 


THE    UNIVERSE    AS    AN    ORGANISM 

activity,  and  the  formation  of  nebulous  masses 
around  the  new  stars,  can  be  accounted  for  only  by 
emanations  or  forms  of  force,  having  probably  some 
similarity  with  the  corpuscles,  electrons,  and  rays 
which  we  are  now  producing  in  our  laboratories.  The 
nineteenth  century,  in  passing  away,  points  with 
pride  to  what  it  has  done.  It  has  become  a  word  to 
symbolize  what  is  most  important  in  human  progress. 
Yet,  perhaps  its  greatest  glory  may  prove  to  be  that 
the  last  thing  it  did  was  to  lay  a  foundation  for  the 
physical  science  of  the  twentieth  century.  What  shall 
be  discovered  in  the  new  fields  is,  at  present,  as  far 
without  our  ken  as  were  the  modern  developments 
of  electricity  without  the  ken  of  the  investigators  of 
one  hundred  years  ago.  We  cannot  guarantee  any 
special  discovery.  What  lies  before  us  is  an  illimit- 
able field,  the  existence  of  which  was  scarcely  sus- 
pected ten  years  ago,  the  exploration  of  which  may 
well  absorb  the  activities  of  our  physical  laboratories, 
and  of  the  great  mass  of  our  astronomical  observers 
and  investigators  for  as  many  generations  as  were 
required  to  bring  electrical  science  to  its  present  state. 
We  of  the  older  generation  cannot  hope  to  see  more 
than  the  beginning  of  this  development,  and  can  only 
tender  our  best  wishes  and  most  hearty  congratula- 
tions to  the  younger  school  whose  function  it  will  be 
to  explore  the  limitless  field  now  before  it. 

M 


XX 

THE    RELATION    OF    SCIENTIFIC    METHOD    TO 
SOCIAL    PROGRESS* 

A¥ONG  those  subjects  which  are  not  always  cor- 
rectly apprehended,  even  by  educated  men,  we 
may  place  that  of  the  true  significance  of  scientific 
method  and  the  relations  of  such  method  to  practical 
affairs.  This  is  especially  apt  to  be  the  case  in  a 
country  like  our  own,  where  the  points  of  contact 
between  the  scientific  world  on  the  one  hand,  and  the 
industrial  and  political  world  on  the  other,  are  fewer 
than  in  other  civilized  countries.  The  form  which 
this  misapprehension  usually  takes  is  that  of  a  failure 
to  appreciate  the  character  of  scientific  method,  and 
especially  its  analogy  to  the  methods  of  practical  life. 
In  the  judgment  of  the  ordinary  intelligent  man 
there  is  a  wide  distinction  between  theoretical  and 
practical  science.  The  latter  he  considers  as  that 
science  directly  applicable  to  the  building  of  railroads, 
the  construction  of  engines,  the  invention  of  new 
machinery,  the  construction  of  maps,  and  other  use- 
ful objects.  The  former  he  considers  analogous  to 
those  philosophic  speculations  in  which  men  have  in- 
dulged in  all  ages  without  leading  to  any  result  which 
he  considers  practical.  That  our  knowledge  of  nature 
is  increased  by  its  prosecution  is  a  fact  of  which  he  is 

*  An  address  before  the  Washington  Philosophical  Society. 
312 


SCIENTIFIC    METHOD 

quite  conscious,  but  he  considers  it  a's  terminating 
with  a  mere  increase  of  knowledge,  and  not  as  having 
in  its  method  anything  which  a  person  devoted  to 
material  interests  can  be  expected  to  appreciate. 

This  view  is  strengthened  by  the  spirit  with  which 
he  sees  scientific  investigation  prosecuted.  It  is  well 
understood  on  all  sides  that  when  such  investigations 
are  pursued  in  a  spirit  really  recognized  as  scientific, 
no  merely  utilitarian  object  is  had  in  view.  Indeed, 
it  is  easy  to  see  how  the  very  fact  of  pursuing  such 
an  object  would  detract  from  that  thoroughness  of 
examination  which  is  the  first  condition  of  a  real  ad- 
vance. True  science  demands  in  its  every  research 
a  completeness  far  beyond  what  is  apparently  neces- 
sary for  its  practical  applications.  The  precision 
with  which  the  astronomer  seeks  to  measure  the 
heavens  and  the  chemist  to  determine  the  relations 
of  the  ultimate  molecules  of  matter  has  no  limit,  ex- 
cept that  set  by  the  imperfections  of  the  instruments 
of  research.  There  is  no  such  division  recognized  as 
that  of  useful  and  useless  knowledge.  The  ultimate 
aim  is  nothing  less  than  that  of  bringing  all  the 
phenomena  of  nature  under  laws  as  exact  as  those 
which  govern  the  planetary  motions. 

Now  the  pursuit  of  any  high  object  in  this  spirit 
commands  from  men  of  wide  views  that  respect  which 
is  felt  towards  all  exertion  having  in  view  more  ele- 
vated objects  than  the  pursuit  of  gain.  Accordingly, 
it  is  very  natural  to  classify  scientists  and  philoso- 
phers with  the  men  who  in  all  ages  have  sought  after 
learning  instead  of  utility.  But  there  is  another 
aspect  of  the  question  which  will  show  the  relations 
of  scientific  advance  to  the  practical  affairs  of  life 
in  a  different  light.  I  make  bold  to  say  that  the 

313 


SIDE-LIGHTS    ON    ASTRONOMY 

greatest  want  of  the  day,  from  a  purely  practical 
point  of  view,  is  the  more  general  introduction  of  the 
scientific  method  and  the  scientific  spirit  into  the 
discussion  of  those  political  and  social  problems  which 
we  encounter  on  our  road  to  a  higher  plane  of  public 
well  being.  Far  from  using  methods  too  refined  for 
practical  purposes,  what  most  distinguishes  scientific 
from  other  thought  is  the  introduction  of  the  methods 
of  practical  life  into  the  discussion  of  abstract  general 
problems.  A  single  instance  will  illustrate  the  lesson 
I  wish  to  enforce. 

The  question  of  the  tariff  is,  from  a  practical  point 
of  view,  one  of  the  most  important  with  which  our 
legislators  will  have  to  deal  during  the  next  few 
years.  The  widest  diversity  of  opinion  exists  as  to 
the  best  policy  to  be  pursued  in  collecting  a  revenue 
from  imports.  Opposing  interests  contend  against 
one  another  without  any  common  basis  of  fact  or  prin- 
ciple on  which  a  conclusion  can  be  reached.  The 
opinions  of  intelligent  men  differ  almost  as  widely 
as  those  of  the  men  who  are  immediately  interested. 
But  all  will  admit  that  public  action  in  this  direction 
should  be  dictated  by  one  guiding  principle — that 
the  greatest  good  of  the  community  is  to  be  sought 
after.  That  policy  is  the  best  which  will  most  pro- 
mote this  good.  Nor  is  there  any  serious  difference 
of  opinion  as  to  the  nature  of  the  good  to  be  had  in 
view;  it  is  in  a  word  the  increase  of  the  national 
wealth  and  prosperity.  The  question  on  which  opin- 
ions fundamentally  differ  is  that  of  the  effects  of  a 
higher  or  lower  rate  of  duty  upon  the  interests  of  the 
public.  If  it  were  possible  to  foresee,  with  an  ap- 
proach to  certainty,  what  effect  a  given  tariff  would 
have  upon  the  producers  and  consumers  of  an  article 

3M 


SCIENTIFIC    METHOD 

taxed,  and,  indirectly,  upon  each  member  of  the  com- 
munity in  any  way  interested  in  the  article,  we  should 
then  have  an  exact  datum  which  we  do  not  now  pos- 
sess for  reaching  a  conclusion.  If  some  superhuman 
authority,  speaking  with  the  voice  of  infallibility, 
could  give  us  this  information,  it  is  evident  that  a 
great  national  want  would  be  supplied.  No  question 
in  practical  life  is  more  important  than  this:  How 
can  this  desirable  knowledge  of  the  economic  effects 
of  a  tariff  be  obtained  ? 

The  answer  to  this  question  is  clear  and  simple. 
The  subject  must  be  studied  in  the  same  spirit,  and, 
to  a  certain  extent,  by  the  same  methods  which  have 
been  so  successful  in  advancing  our  knowledge  of 
nature.  Every  one  knows  that,  within  the  last  two 
centuries,  a  method  of  studying  the  course  of  nature 
has  been  introduced  which  has  been  so  successful  in 
enabling  us  to  trace  the  sequence  of  cause  and  effect 
as  almost  to  revolutionize  society.  The  very  fact 
that  scientific  method  has  been  so  successful  here 
leads  to  the  belief  that  it  might  be  equally  successful 
in  other  departments  of  inquiry. 

The  same  remarks  will  apply  to  the  questions  con- 
nected with  banking  and  currency;  the  standard  of 
value;  and,  indeed,  all  subjects  which  have  a  financial 
bearing.  On  every  such  question  we  see  wide  dif- 
ferences of  opinion  without  any  common  basis  to  rest 
upon. 

It  may  be  said,  in  reply,  that  in  these  cases  there 
are  really  no  grounds  for  forming  an  opinion,  and 
that  the  contests  which  arise  over  them  are  merely 
those  between  conflicting  interests.  But  this  claim 
is  not  at  all  consonant  with  the  form  which  we  see 
the  discussion  assume.  Nearly  every  one  has  a  de- 


SIDE-LIGHTS    ON    ASTRONOMY 

cided  opinion  on  these  several  subjects;  whereas,  if 
there  were  no  data  for  forming  an  opinion,  it  would 
be  unreasonable  to  maintain  any  whatever.  Indeed, 
it  is  evident  that  there  must  be  truth  somewhere, 
and  the  only  question  that  can  be  open  is  that  of 
the  mode  of  discovering  it.  No  man  imbued  with 
a  scientific  spirit  can  claim  that  such  truth  is  beyond 
the  power  of  the  human  intellect.  He  may  doubt 
his  own  ability  to  grasp  it,  but  cannot  doubt  that  by 
pursuing  the  proper  method  and  adopting  the  best 
means  the  problem  can  be  solved.  It  is,  in  fact, 
difficult  to  show  why  some  exact  results  could  not  be 
as  certainly  reached  in  economic  questions  as  in 
those  of  physical  science.  It  is  true  that  if  we  pursue 
the  inquiry  far  enough  we  shall  find  more  complex 
conditions  to  encounter,  because  the  future  course 
of  demand  and  supply  enters  as  an  uncertain  element. 
But  a  remarkable  fact  to  be  considered  is  that  the 
difference  of  opinion  to  which  we  allude  does  not  de- 
pend upon  different  estimates  of  the  future,  but  upon 
different  views  of  the  most  elementary  and  general 
principles  of  the  subject.  It  is  as  if  men  were  not 
agreed  whether  air  were  elastic  or  whether  the  earth 
turns  on  its  axis.  Why  is  it  that  while  in  all  subjects 
of  physical  science  we  find  a  general  agreement 
through  a  wide  range  of  subjects,  and  doubt  com- 
mences only  where  certainty  is  not  attained,  yet  when 
we  turn  to  economic  subjects  we  do  not  find  the  be- 
ginning of  an  agreement? 

No  two  answers  can  be  given.  It  is  because  the 
two  classes  of  subjects  are  investigated  by  different 
instruments  and  in  a  different  spirit.  The  physicist 
has  an  exact  nomenclature;  uses  methods  of  research 
well  adapted  to  the  objects  he  has  in  view;  pursues 

316 


SCIENTIFIC    METHOD 

his  investigations  without  being  attacked  by  those 
who  wish  for  different  results ;  and,  above  all,  pursues 
them  only  for  the  purpose  of  discovering  the  truth. 
In  economic  questions  the  case  is  entirely  different. 
Only  in  rare  cases  are  they  studied  without  at  least 
the  suspicion  that  the  student  has  a  preconceived 
theory  to  support.  If  results  are  attained  which  op- 
pose any  powerful  interest,  this  interest  can  hire  a 
competing  investigator  to  bring  out  a  different  result. 
So  far  as  the  public  can  see,  one  man's  result  is  as 
good  as  another's,  and  thus  the  object  is  as  far  off 
as  ever.  We  may  be  sure  that  until  there  is  an  in- 
telligent and  rational  public,  able  to  distinguish  be- 
tween the  speculations  of  the  charlatan  and  the  re- 
searches of  the  investigator,  the  present  state  of 
things  will  continue.  What  we  want  is  so  wide  a 
diffusion  of  scientific  ideas  that  there  shall  be  a  class 
of  men  engaged  in  studying  economic  problems  for 
their  own  sake,  and  an  intelligent  public  able  to 
judge  what  they  are  doing.  There  must  be  an  im- 
provement in  the  objects  at  which  they  aim  in  educa- 
tion, and  it  is  now  worth  while  to  inquire  what  that 
improvement  is. 

It  is  not  mere  instruction  in  any  branch  of  technical 
science  that  is  wanted.  No  knowledge  of  chemistry, 
physics,  or  biology,  however  extensive,  can  give  the 
learner  much  aid  in  forming  a  correct  opinion  of  such 
a  question  as  that  of  the  currency.  If  we  should 
claim  that  political  economy  ought  to  be  more  ex- 
tensively studied,  we  would  be  met  by  the  question, 
which  of  several  conflicting  systems  shall  we  teach? 
What  is  wanted  is  not  to  teach  this  system  or  that, 
but  to  give  such  a  training  that  the  student  shall  be 
able  to  decide  for  himself  which  system  is  right. 


SIDE-LIGHTS    ON    ASTRONOMY 

It  seems  to  me  that  the  true  educational  want  is 
ignored  both  by  those  who  advocate  a  classical  and 
those  who  advocate  a  scientific  education.  What  is 
really  wanted  is  to  train  the  intellectual  powers,  and 
the  question  ought  to  be,  what  is  the  best  method  of 
doing  this?  Perhaps  it  might  be  found  that  both  of 
the  conflicting  methods  could  be  improved  upon. 
The  really  distinctive  features,  which  we  should  de- 
sire to  see  introduced,  are  two  in  number:  the  one  the 
scientific  spirit ;  the  other  the  scientific  discipline.  Al- 
though many  details  may  be  classified  under  each  of 
these  heads,  yet  there  is  one  of  pre-eminent  impor- 
tance on  which  we  should  insist. 

The  one  feature  of  the  scientific  spirit  which  out- 
weighs all  others  in  importance  is  the  love  of  knowl- 
edge for  its  own  sake.  If  by  our  system  of  education 
we  can  inculcate  this  sentiment  we  shall  do  what  is, 
from  a  public  point  of  view,  worth  more  than  any 
amount  of  technical  knowledge,  because  we  shall  lay 
the  foundation  of  all  knowledge.  So  long  as  men 
study  only  what  they  think  is  going  to  be  useful 
their  knowledge  will  be  partial  and  insufficient.  I 
think  it  is  to  the  constant  inculcation  of  this  fact  by 
experience,  rather  than  to  any  reasoning,  that  is 
due  the  continued  appreciation  of  a  liberal  education. 
Every  business -man  knows  that  a  business -college 
training  is  of  very  little  account  in  enabling  one  to 
fight  the  battle  of  life,  and  that  college -bred  men 
have  a  great  advantage  even  in  fields  where  mere 
education  is  a  secondary  matter.  We  are  accustomed 
to  seeing  ridicule  thrown  upon  the  questions  some- 
times asked  of  candidates  for  the  civil  service  because 
the  questions  refer  to  subjects  of  which  a  knowledge 
is  not  essential.  The  reply  to  all  criticisms  of  this 

318 


SCIENTIFIC    METHOD 

kind  is  that  there  is  no  one  quality  which  more  cer- 
tainly assures  a  man's  usefulness  to  society  than  the 
propensity  to  acquire  useless  knowledge.  Most  of 
our  citizens  take  a  wide  interest  in  public  affairs,  else 
our  form  of  government  would  be  a  failure.  But  it 
is  desirable  that  their  study  of  public  measures  should 
be  more  critical  and  take  a  wider  range.  It  is  espe- 
cially desirable  that  the  conclusions  to  which  they 
are  led  should  be  unaffected  by  partisan  sympathies. 
The  more  strongly  the  love  of  mere  truth  is  in- 
culcated in  their  nature  the  better  this  end  will  be 
attained . 

The  scientific  discipline  to  which  I  ask  mainly  to 
call  your  attention  consists  in  training  the  scholar 
to  the  scientific  use  of  language.  Although  whole 
volumes  may  be  written  on  the  logic  of  science  there 
is  one  general  feature  of  its  method  which  is  of  funda- 
mental significance.  It  is  that  every  term  which  it 
uses  and  every  proposition  which  it  enunciates  has 
a  precise  meaning  which  can  be  made  evident  by 
proper  definitions.  This  general  principle  of  scientific 
language  is  much  more  easily  inculcated  by  example 
than  subject  to  exact  description ;  but  I  shall  ask  leave 
to  add  one  to  several  attempts  I  have  made  to  define 
it.  If  I  should  say  that  when  a  statement  is  made  in 
the  language  of  science  the  speaker  knows  what  he 
means,  and  the  hearer  either  knows  it  or  can  be  made 
to  know  it  by  proper  definitions,  and  that  this  com- 
munity of  understanding  is  frequently  not  reached 
in  other  departments  of  thought,  I  might  be  under- 
stood as  casting  a  slur  on  whole  departments  of  in- 
quiry. Without  intending  any  such  slur,  I  may  still 
say  that  language  and  statements  are  worthy  of  the 
name  scientific  as  they  approach  this  standard ;  and, 

3*9 


SIDE-LIGHTS    ON    ASTRONOMY 


moreover,  that  a  great  deal  is  said  and  written  which 
does  not  fulfil  the  requirement.  The  fact  that  words 
lose  their  meaning  when  removed  from  the  connec- 
tions in  which  that  meaning  has  been  acquired  and 
put  to  higher  uses,  is  one  which,  I  think,  is  rarely 
recognized.  There  is  nothing  in  the  history  of  philo- 
sophical inquiry  more  curious  than  the  frequency  of 
interminable  disputes  on  subjects  where  no  agree- 
ment can  be  reached  because  the  opposing  parties 
do  not  use  words  in  the  same  sense.  That  the  history 
of  science  is  not  free  from  this  reproach  is  shown  by 
the  fact  of  the  long  dispute  whether  the  force  of  a 
moving  body  was  proportional  to  the  simple  velocity 
or  to  its  square.  Neither  of  the  parties  to  the  dispute 
thought  it  worth  while  to  define  what  they  meant 
by  the  word  "  force,"  and  it  was  at  length  found  that 
if  a  definition  was  agreed  upon  the  seeming  difference 
of  opinion  would  vanish.  Perhaps  the  most  striking 
feature  of  the  case,  and  one  peculiar  to  a  scientific 
dispute,  was  that  the  opposing  parties  did  not  differ 
in  their  solution  of  a  single  mechanical  problem.  I 
say  this  is  curious,  because  the  very  fact  of  their 
agreeing  upon  every  concrete  question  which  could 
have  been  presented  ought  to  have  made  it  clear  that 
some  fallacy  was  lacking  in  the  discussion  as  to  the 
measure  of  force.  The  good  effect  of  a  scientific 
spirit  is  shown  by  the  fact  that  this  discussion  is  al- 
most unique  in  the  history  of  science  during  the 
past  two  centuries,  and  that  scientific  men  themselves 
were  able  to  see  the  fallacy  involved,  and  thus  to  bring 
the  matter  to  a  conclusion. 

If  we  now  turn  to  the  discussion  of  philosophers, 
we  shall  find  at  least  one  yet  more  striking  example 
of  the  same  kind.  The  question  of  the  freedom  of 

320 


SCIENTIFIC    METHOD 

the  human  will  has,  I  believe,  raged  for  centuries. 
It  cannot  yet  be  said  that  any  conclusion  has  been 
reached.  Indeed,  I  have  heard  it  admitted  by  men 
of  high  intellectual  attainments  that  the  question 
was  insoluble.  Now  a  curious  feature  of  this  dis- 
pute is  that  none  of  the  combatants,  at  least  on  the 
affirmative  side,  have  made  any  serious  attempt  to 
define  what  should  be  meant  by  the  phrase  freedom 
of  the  will,  except  by  using  such  terms  as  require 
definition  equally  with  the  word  freedom  itself.  It 
can,  I  conceive,  be  made  quite  clear  that  the  assertion, 
"The  will  is  free,"  is  one  without  meaning,  until  we 
analyze  more  fully  the  different  meanings  to  be  at- 
tached to  the  word  free.  Now  this  word  has  a  per- 
fectly well-defined  signification  in  every -day  life. 
We  say  that  anything  is  free  when  it  is  not  subject 
to  external  constraint.  We  also  know  exactly  what 
we  mean  when  we  say  that  a  man  is  free  to  do  a  cer- 
tain act.  We  mean  that  if  he  chooses  to  do  it  there 
is  no  external  constraint  acting  to  prevent  him.  In 
all  cases  a  relation  of  two  things  is  implied  in  the 
word,  some  active  agent  or  power,  and  the  presence 
or  absence  of  another  constraining  agent.  Now, 
when  we  inquire  whether  the  will  itself  is  free,  ir- 
respective of  external  constraints,  the  word  free  no 
longer  has  a  meaning,  because  one  of  the  elements 
implied  in  it  is  ignored. 

To  inquire  whether  the  will  itself  is  free  is  like 
inquiring  whether  fire  itself  is  consumed  by  the  burn- 
ing, or  whether  clothing  is  itself  clad.  It  is  not, 
therefore,  at  all  surprising  that  both  parties  have 
been  able  to  dispute  without  end,  but  it  is  a  most 
astonishing  phenomenon  of  the  human  intellect  that 
the  dispute  should  go  on  generation  after  generation 

321 


SIDE-LIGHTS    ON    ASTRONOMY 

without  the  parties  finding  out  whether  there  was 
really  any  difference  of  opinion  between  them  on  the 
subject.  I  venture  to  say  that  if  there  is  any  such 
difference,  neither  party  has  ever  analyzed  the  mean- 
ing of  the  words  used  sufficiently  far  to  show  it. 
The  daily  experience  of  every  man,  from  his  cradle 
to  his  grave,  shows  that  human  acts  are  as  much 
the  subject  of  external  causal  influences  as  are  the 
phenomena  of  nature.  To  dispute  this  would  be 
little  short  of  the  ludicrous.  All  that  the  opponents 
of  freedom,  as  a  class,  have  ever  claimed  is  the  as- 
sertion of  a  causal  connection  between  the  acts  of  the 
will  and  influences  independent  of  the  will.  True, 
propositions  of  this  sort  can  be  expressed  in  a  variety 
of  ways  connoting  an  endless  number  of  more  or  less 
objectionable  ideas,  but  this  is  the  substance  of  the 
matter. 

To  suppose  that  the  advocates  on  the  other  side 
meant  to  take  issue  on  this  proposition  would  be  to 
assume  that  they  did  not  know  what  they  were  say- 
ing. The  conclusion  forced  upon  us  is  that  though 
men  spend  their  whole  lives  in  the  study  of  the  most 
elevated  department  of  human  thought  it  does  not 
guard  them  against  the  danger  of  using  words  with- 
out meaning.  It  would  be  a  mark  of  ignorance, 
rather  than  of  penetration,  to  hastily  denounce  prop- 
ositions on  subjects  we  are  not  well  acquainted  with 
because  we  do  not  understand  their  meaning.  I  do 
not  mean  to  intimate  that  philosophy  itself  is  sub- 
ject to  this  reproach.  When  we  see  a  philosophical 
proposition  couched  in  terms  we  do  not  understand, 
the  most  modest  and  charitable  view  is  to  assume 
that  this  arises  from  our  lack  of  knowledge.  Noth- 
ing is  easier  than  for  the  ignorant  to  ridicule  the 

322 


SCIENTIFIC    METHOD 

propositions  of  the  learned.  And  yet,  with  every 
reserve,  I  cannot  but  feel  that  the  disputes  to  which 
I  have  alluded  prove  the  necessity  of  bringing  scien- 
tific precision  of  language  into  the  whole  domain  of 
thought.  If  the  discussion  had  been  confined  to  a 
few,  and  other  philosophers  had  analyzed  the  sub- 
ject, and  showed  the  fictitious  character  of  the  dis- 
cussion, or  had  pointed  out  where  opinions  really 
might  differ,  there  would  be  nothing  derogatory  to 
philosophers.  But  the  most  suggestive  circum- 
stance is  that  although  a  large  proportion  of  the 
philosophic  writers  in  recent  times  have  devoted 
more  or  less  attention  to  the  subject,  few,  or  none, 
have  made  even  this  modest  contribution.  I  speak 
with  some  little  confidence  on  this  subject,  because 
several  years  ago  I  wrote  to  one  of  the  most  acute 
thinkers  of  the  country,  asking  if  he  could  find  in 
philosophic  literature  any  terms  or  definitions  ex- 
pressive of  the  three  different  senses  in  which  not 
only  the  word  freedom,  but  nearly  all  words  implying 
freedom  were  used.  His  search  was  in  vain. 

Nothing  of  this  sort  occurs  in  the  practical  affairs 
of  life.  All  terms  used  in  business,  however  general 
or  abstract,  have  that  well-defined  meaning  which  is 
the  first  requisite  of  the  scientific  language.  Now 
one  important  lesson  which  I  wish  to  inculcate  is 
that  the  language  of  science  in  this  respect  corre- 
sponds to  that  of  business;  in  that  each  and  every 
term  that  is  employed  has  a  meaning  as  well  defined 
as  the  subject  of  discussion  can  admit  of.  It  will 
be  an  instructive  exercise  to  inquire  what  this  pe- 
culiarity of  scientific  and  business  language  is.  It 
can  be  shown  that  a  certain  requirement  should  be 
fulfilled  by  all  language  intended  for  the  discovery 

323 


SIDE-LIGHTS    ON    ASTRONOMY 

of  truth,  which  is  fulfilled  only  by  the  two  classes  of 
language  which  I  have  described.  It  is  one  of  the 
most  common  errors  of  discourse  to  assume  that  any 
common  expression  which  we  may  use  always  conveys 
an  idea,  no  matter  what  the  subject  of  discourse. 
The  true  state  of  the  case  can,  perhaps,  best  be  seen 
by  beginning  at  the  foundation  of  things  and  ex- 
amining under  what  conditions  language  can  really 
convey  ideas. 

.  Suppose  thrown  among  us  a  person  of  well-devel- 
oped intellect,  but  unacquainted  with  a  single  lan- 
guage or  word  that  we  use.  It  is  absolutely  useless 
to  talk  to  him,  because  nothing  that  we  say  conveys 
any  meaning  to  his  mind.  We  can  supply  him  no 
dictionary,  because  by  hypothesis  he  knows  no 
language  to  which  we  have  access.  How  shall  we 
proceed  to  communicate  our  ideas  to  him?  Clearly 
there  is  but  one  possible  way — namely,  through  his 
senses.  Outside  of  this  means  of  bringing  him  in 
contact  with  us  we  can  have  no  communication 
with  him.  We,  therefore,  begin  by  showing  him 
sensible  objects,  and  letting  him  understand  that 
certain  words  which  we  use  correspond  to  those  ob- 
jects. After  he  has  thus  acquired  a  small  vocabulary, 
we  make  him  understand  that  other  terms  refer  to 
relations  between  objects  which  he  can  perceive  by 
his  senses.  Next  he  learns,  by  induction,  that  there 
are  terms  which  apply  not  to  special  objects,  but  to 
whole  classes  of  objects.  Continuing  the  same  proc- 
ess, he  learns  that  there  are  certain  attributes  of 
objects  made  known  by  the  manner  in  which  they 
affect  his  senses,  to  which  abstract  terms  are  applied. 
Having  learned  all  this,  we  can  teach  him  new  words 
by  combining  words  without  exhibiting  objects  al- 

324 


SCIENTIFIC    METHOD 

ready  known.  Using  these  words  we  can  proceed 
yet  further,  building  up,  as  it  were,  a  complete  lan- 
guage. But  there  is  one  limit  at  every  step.  Every 
term  which  we  make  known  to  him  must  depend 
ultimately  upon  terms  the  meaning  of  which  he  has 
learned  from  their  connection  with  special  objects 
of  sense. 

To  communicate  to  him  a  knowledge  of  words  ex- 
pressive of  mental  states  it  is  necessary  to  assume 
that  his  own  mind  is  subject  to  these  states  as  well  as 
our  own,  and  that  we  can  in  some  way  indicate  them 
by  our  acts.  That  the  former  hypothesis  is  suffi- 
ciently well  established  can  be  made  evident  so  long 
as  a  consistency  of  different  words  and  ideas  is  main- 
tained. If  no  such  consistency  of  meaning  on  his 
part  were  evident,  it  might  indicate  that  the  opera- 
tions of  his  mind  were  so  different  from  ours  that 
no  such  communication  of  ideas  was  possible.  Un- 
certainty in  this  respect  must  arise  as  soon  as  we  go 
beyond  those  mental  states  which  communicate 
themselves  to  the  senses  of  others. 

We  now  see  that  in  order  to  communicate  to  our 
foreigner  a  knowledge  of  language,  we  must  follow 
rules  similar  to  those  necessary  for  the  stability  of  a 
building.  The  foundation  of  the  building  must  be 
well  laid  upon  objects  knowable  by  his  five  senses. 
Of  course  the  mind,  as  well  as  the  external  object, 
may  be  a  factor  in  determining  the  ideas  which  the 
words  are  intended  to  express;  but  this  does  not  in 
any  manner  invalidate  the  conditions  which  we  im- 
pose. Whatever  theory  we  may  adopt  of  the  relative 
part  played  by  the  knowing  subject,  and  the  external 
object  in  the  acquirement  of  knowledge,  it  remains 
none  the  less  true  that  no  knowledge  of  the  meaning 

325 


SIDE-LIGHTS    ON    ASTRONOMY 

of  a  word  can  be  acquired  except  through  the  senses, 
and  that  the  meaning  is,  therefore,  limited  by  the 
senses.  If  we  transgress  the  rule  of  founding  each 
meaning  upon  meanings  below  it,  and  having  the 
whole  ultimately  resting  upon  a  sensuous  foundation, 
we  at  once  branch  off  into  sound  without  sense.  We 
may  teach  him  the  use  of  an  extended  vocabulary, 
to  the  terms  of  which  he  may  apply  ideas  of  his  own, 
more  or  less  vague,  but  there  will  be  no  way  of  de- 
ciding that  he  attaches  the  same  meaning  to  these 
terms  that  we  do. 

What  we  have  shown  true  of  an  intelligent  foreigner 
is  necessarily  true  of  the  growing  child.  We  come 
into  the  world  without  a  knowledge  of  the  meaning 
of  words,  and  can  acquire  such  knowledge  only  by 
a  process  which  we  have  found  applicable  to  the  in- 
telligent foreigner.  But  to  confine  ourselves  within 
these  limits  in  the  use  of  language  requires  a  course 
of  severe  mental  discipline.  The  transgression  of 
the  rule  will  naturally  seem  to  the  undisciplined 
mind  a  mark  of  intellectual  vigor  rather  than  the  re- 
verse. In  our  system  of  education  every  temptation 
is  held  out  to  the  learner  to  transgress  the  rule  by 
the  fluent  use  of  language  to  which  it  is  doubtful  if 
he  himself  attaches  clear  notions,  and  which  he  can 
never  be  certain  suggests  to  his  hearer  the  ideas 
which  he  desires  to  convey.  Indeed,  we  not  infre- 
quently see,  even  among  practical  educators,  ex- 
pressions of  positive  antipathy  to  scientific  precision 
of  language  so  obviously  opposed  to  good  sense  that 
they  can  be  attributed  only  to  a  failure  to  compre- 
hend the  meaning  of  the  language  which  they  criticise. 

Perhaps  the  most  injurious  effect  in  this  direction 
arises  from  the  natural  tendency  of  the  mind,  when 

326 


SCIENTIFIC    METHOD 

not  subject  to  a  scientific  discipline,  to  think  of  words 
expressing  sensible  objects  and  their  relations  as 
connoting  certain  supersensuous  attributes.  This  is 
frequently  seen  in  the  repugnance  of  the  metaphysical 
mind  to  receive  a  scientific  statement  about  a  matter 
of  fact  simply  as  a  matter  of  fact.  This  repugnance 
does  not  generally  arise  in  respect  to  the  every-day 
matters  of  life.  Wh£n  we  say  that  the  earth  is  round 
we  state  a  truth  which  every  one  is  willing  to  receive 
as  final.  If  without  denying  that  the  earth  was 
round,  one  should  criticise  the  statement  on  the 
ground  that  it  was  not  necessarily  round  but  might 
be  of  some  other  form,  we  should  simply  smile  at 
this  use  of  language.  But  when  we  take  a  more 
general  statement  and  assert  that  the  laws  of  nature 
are  inexorable,  and  that  all  phenomena,  so  far  as 
we  can  show,  occur  in  obedience  to  their  requirements, 
we  are  met  with  a  sort  of  criticism  with  which  all  of 
us  are  familiar,  but  which  I  am  unable  adequately  to 
describe.  No  one  denies  that  as  a  matter  of  fact, 
and  as  far  as  his  experience  extends,  these  laws  do 
appear  to  be  inexorable.  I  have  never  heard  of  any 
one  professing,  during  the  present  generation,  to  de- 
scribe a  natural  phenomenon,  with  the  avowed  belief 
that  it  was  not  a  product  of  natural  law ;  yet  we  con- 
stantly hear  the  scientific  view  criticised  on  the 
ground  that  events  may  occur  without  being  subject 
to  natural  law.  The  word  "  may,"  in  this  connection, 
is  one  to  which  we  can  attach  no  meaning  expressive 
of  a  sensuous  relation. 

The  analogous  conflict  between  the  scientific  use 
of  language  and  the  use  made  by  some  philosophers 
is  found  in  connection  with  the  idea  of  causation. 
Fundamentally  the  word  cause  is  used  in  scientific 

aa  327 


SIDE-LIGHTS    ON    ASTRONOMY 

language  in  the  same  sense  as  in  the  language  of 
common  life.  When  we  discuss  with  our  neighbors 
the  cause  of  a  fit  of  illness,  of  a  fire,  or  of  cold  weather, 
not  the  slightest  ambiguity  attaches  to  the  use  of  the 
word,  because  whatever  meaning  may  be  given  to 
it  is  founded  only  on  an  accurate  analysis  of  the 
ideas  involved  in  it  from  daily  ^use.  No  philosopher 
objects  to  the  common  meaning  of  the  word,  yet  we 
frequently  find  men  of  eminence  in  the  intellectual 
world  who  will  not  tolerate  the  scientific  man  in 
using  the  word  in  this  way.  In  every  explanation 
which  he  can  give  to  its  use  they  detect  ambiguity. 
They  insist  that  in  any  proper  use  of  the  term  the 
idea  of  power  must  be  connoted.  But  what  meaning 
is  here  attached  to  the  word  power,  and  how  shall 
we  first  reduce  it  to  a  sensible  form,  and  then  apply 
its  meaning  to  the  operations  of  nature?  Whether 
this  can  be  done,  I  do  not  inquire.  All  I  maintain 
is  that  if  we  wish  to  do  it,  we  must  pass  without  the 
domain  of  scientific  statement. 

Perhaps  the  greatest  advantage  in  the  use  of  sym- 
bolic and  other  mathematical  language  in  scientific 
investigation  is  that  it  cannot  possibly  be  made  to 
connote  anything  except  what  the  speaker  means. 
It  adheres  to  the  subject  matter  of  discourse  with  a 
tenacity  which  no  criticism  can  overcome.  In  con- 
sequence, whenever  a  science  is  reduced  to  a  mathe- 
matical form  its  conclusions  are  no  longer  the  subject 
of  philosophical  attack.  To  secure  the  same  desir- 
able quality  in  all  other  scientific  language  it  is  neces- 
sary to  give  it,  so  far  as  possible,  the  same  simplicity 
of  signification  which  attaches  to  mathematical  sym- 
bols. This  is  not  easy,  because  we  are  obliged  to 
use  words  of  ordinary  language,  and  it  is  impossible 

328 


SCIENTIFIC    METHOD 

to  divest  them  of  whatever  they  may  connote  to 
ordinary  hearers. 

I  have  thus  sought  to  make  it  clear  that  the  lan- 
guage of  science  corresponds  to  that  of  ordinary  life, 
and  especially  of  business  life,  in  confining  its  mean- 
ing to  phenomena.  An  analogous  statement  may 
be  made  of  the  method  and  objects  of  scientific  in- 
vestigation. I  think  Professor  Clifford  was  very 
happy  in  defining  science  as  organized  common-sense. 
The  foundation  of  its  widest  general  creations  is  laid, 
not  in  any  artificial  theories,  but  in  the  natural  be- 
liefs and  tendencies  of  the  human  mind.  Its  position 
against  those  who  deny  these  generalizations  is  quite 
analogous  to  that  taken  by  the  Scottish  school  of 
philosophy  against  the  scepticism  of  Hume. 

It  may  be  asked,  if  the  methods  and  language  of 
science  correspond  to  those  of  practical  life,  why  is 
not  the  every-day  discipline  of  that  life  as  good  as 
the  discipline  of  science?  The  answer  is,  that  the 
power  of  transferring  the  modes  of  thought  of  com- 
mon life  to  subjects  of  a  higher  order  of  generality  is 
a  rare  faculty  which  can  be  acquired  only  by  scientific 
discipline.  What  we  want  is  that  in  public  affairs 
men  shall  reason  about  questions  of  finance,  trade, 
national  wealth,  legislation,  and  administration,  with 
the  same  consciousness  of  the  practical  side  that 
they  reason  about  their  own  interests.  When  this 
habit  is  once  acquired  and  appreciated,  the  scientific 
method  will  naturally  be  applied  to  the  study  of 
questions  of  social  policy.  When  a  scientific  interest 
is  taken  in  such  questions,  their  boundaries  will  be 
extended  beyond  the  utilities  immediately  involved, 
and  one  important  condition  of  unceasing  progress 
will  be  complied  with. 

329 


XXI 

THE   OUTLOOK   FOR  THE   FLYING-MACHINE 

MR.  SECRETARY  LANGLEY'S  trial  of  his  flying- 
machine,  which  seems  to  have  come  to  an  abor- 
tive issue  for  the  time,  strikes  a  sympathetic  chord 
in  the  constitution  of  our  race.  Are  we  not  the  lords 
of  creation?  Have  we  not  girdled  the  earth  with 
wires  through  which  we  speak  to  our  antipodes  ?  Do 
we  not  journey  from  continent  to  continent  over 
oceans  that  no  animal  can  cross,  and  with  a  speed  of 
which  our  ancestors  would  never  have  dreamed? 
Is  not  all  the  rest  of  the  animal  creation  so  far  infer- 
ior to  us  in  every  point  that  the  best  thing  it  can  do 
is  to  become  completely  subservient  to  our  needs, 
dying,  if  need  be,  that  its  flesh  may  become  a  tooth- 
some dish  on  our  tables  ?  And  yet  here  is  an  insignif- 
icant little  bird,  from  whose  mind,  if  mind  it  has,  all 
conceptions  of  natural  law  are  excluded,  applying 
the  rules  of  aerodynamics  in  an  application  of  me- 
chanical force  to  an  end  we  have  never  been  able  to 
reach,  and  this  with  entire  ease  and  absence  of  con- 
sciousness that  it  is  doing  an  extraordinary  thing. 
Surely  our  knowledge  of  natural  laws,  and  that  in- 
ventive genius  which  has  enabled  us  to  subordinate 
all  nature  to  our  needs,  ought  also  to  enable  us  to 
do  anything  that  the  bird  can  do.  Therefore  we  must 
fly.  If  we  cannot  yet  do  it,  it  is  only  because  we  have 

330 


THE    FLYING-MACHINE 

not  got  to  the  bottom  of  the  subject.  Our  succes- 
sors of  the  not  distant  future  will  surely  succeed. 

This  is  at  first  sight  a  very  natural  and  plausible 
view  of  the  case.  And  yet  there  are  a  number  of 
circumstances  of  which  we  should  take  account  be- 
fore attempting  a  confident  forecast.  Our  hope  for 
the  future  is  based  on  what  we  have  done  in  the  past. 
But  when  we  draw  conclusions  from  past  successes 
we  should  not  lose  sight  of  the  conditions  on  which 
success  has  depended.  There  is  no  advantage  which 
has  not  its  attendant  drawbacks;  no  strength  which 
has  not  its  concomitant  weakness.  Wealth  has  its 
trials  and  health  its  dangers.  We  must  expect  our 
great  superiority  to  the  bird  to  be  associated  with 
conditions  which  would  give  it  an  advantage  at  some 
point.  A  little  study  will  make  these  conditions  clear. 

We  may  look  on  the  bird  as  a  sort  of  flying-machine 
complete  in  itself,  of  which  a  brain  and  nervous  sys- 
tem are  fundamentally  necessary  parts.  No  such 
machine  can  navigate  the  air  unless  guided  by  some- 
thing having  life.  Apart  from  this,  it  could  be  of 
little  use  to  us  unless  it  carried  human  beings  on  its 
wings.  We  thus  meet  with  a  difficulty  at  the  first 
step — we  cannot  give  a  brain  and  nervous  system  to 
our  machine.  These  necessary  adjuncts  must  be 
supplied  by  a  man,  who  is  ho  part  of  the  machine, 
but  something  carried  by  it.  The  bird  is  a  complete 
machine  in  itself.  Our  aerial  ship  must  be  machine 
plus  man.  Now,  a  man  is,  I  believe,  heavier  than 
any  bird  that  flies.  The  limit  which  the  rarity  of 
the  air  places  upon  its  power  of  supporting  wings, 
taken  in  connection  with  the  combined  weight  of  a 
man  and  a  machine,  make  a  drawback  which  we 
should  not  too  hastily  assume  our  ability  to  overcome, 

331 


SIDE-LIGHTS    ON    ASTRONOMY 

The  example  of  the  bird  does  not  prove  that  man  can 
fly.  The  hundred  and  fifty  pounds  of  dead  weight 
which  the  manager  of  the  machine  must  add  to  it 
over  and  above  that  necessary  in  the  bird  may 'well 
prove  an  insurmountable  obstacle  to  success. 

I  need  hardly  remark  that  the  advantage  possessed 
by  the  bird  has  its  attendant  drawbacks  when  we 
consider  other  movements  than  flying.  Its  wings 
are  simply  one  pair  of  its  legs,  and  the  human  race 
could  not  afford  to  abandon  its  arms  for  the  most 
effective  wings  that  nature  or  art  could  supply. 

Another  point  to  be  considered  is  that  the  bird 
operates  by  the  application  of  a  kind  of  force  which 
is  peculiar  to  the  animal  creation,  and  no  approach 
to  which  has  ever  been  made  in  any  mechanism. 
This  force  is  that  which  gives  rise  to  muscular  action, 
of  which  the  necessary  condition  is  the  direct  action 
of  a  nervous  system.  We  cannot  have  muscles  or 
nerves  for  our  flying-machine.  We  have  to  replace 
them  by  such  crude  and  clumsy  adjuncts  as  steam- 
engines  and  electric  batteries.  It  may  certainly 
seem  singular  if  man  is  never  to  discover  any  com- 
bination of  substances  which,  under  the  influence  of 
some  such  agency  as  an  electric  current,  shall  expand 
and  contract  like  a  muscle.  But,  if  he  is  ever  to  do 
so,  the  time  is  still  in  the  future.  We  do  not  see  the 
dawn  of  the  age  in  which  such  a  result  will  be  brought 
forth. 

Another  consideration  of  a  general  character  may 
be  introduced.  As  a  rule  it  is  the  unexpected  that 
happens  in  invention  as  well  as  discovery.  There 
are  many  problems  which  have  fascinated  mankind 
ever  since  civilization  began  which  we  have  made 
little  or  no  advance  in  solving.  The  only  satisfac- 

332 


THE    FLYING-MACHINE 

tion  we  can  feel  in  our  treatment  of  the  great  geo- 
metrical problems  of  antiquity  is  that  we  have  shown 
their  solution  to  be  impossible.  The  mathematician 
of  to-day  admits  that  he  can  neither  square  the  cir- 
cle, duplicate  the  cube  or  trisect  the  angle.  May 
not  our  mechanicians,  in  like  manner,  be  ultimately 
forced  to  admit  that  aerial  flight  is  one  of  that  great 
class  of  problems  with  which  man  can  never  cope, 
and  give  up  all  attempts  to  grapple  with  it? 

The  fact  is  that  invention  and  discovery  have, 
notwithstanding  their  seemingly  wide  extent,  gone 
on  in  rather  narrower  lines  than  is  commonly  sup- 
posed. If,  a  hundred  years  ago,  the  most  s'agacious 
of  mortals  had  been  told  that  before  the  nineteenth 
century  closed  the  face  of  the  earth  would  be  changed, 
time  and  space  almost  annihilated,  and  communica- 
tion between  continents  made  more  rapid  and  easy 
than  it  was  between  cities  in  his  time ;  and  if  he  had 
been  asked  to  exercise  his  wildest  imagination  in  de- 
picting what  might  come  —  the  airship  and  the  fly- 
ing-machine would  probably  have  had  a  prominent 
place  in  his  scheme,  but  neither  the  steamship,  the 
railway,  the  telegraph,  nor  the  telephone  would  have 
been  there.  Probably  not  a  single  new  agency  which 
he  could  have  imagined  would  have  been  one  that 
has  come  to  pass. 

It  is  quite  clear  to  me  that  success  must  await 
progress  of  a  different  kind  from  that  which  the  in- 
ventors of  flying-machines  are  aiming  at.  We  want 
a  great  discovery,  not  a  great  invention.  It  is  an 
unfortunate  fact  that  we  do  not  always  appreciate 
the  distinction  between  progress  in  scientific  dis- 
covery and  ingenious  application  of  discovery  to 
the  wants  of  civilization.  The  name  of  Marconi  is 

333 


SIDE-LIGHTS    ON    ASTRONOMY 

familiar  to  every  ear;  the  names  of  Maxwell  and 
Herz,  who  made  the  discoveries  which  rendered  wire- 
less telegraphy  possible,  are  rarely  recalled.  Modern 
progress  is  the  result  of  two  factors:  Discoveries  of 
the  laws  of  nature  and  of  actions  or  possibilities  in 
nature,  and  the  application  of  such  discoveries  to 
practical  purposes.  The  first  is  the  work  of  the  scien- 
tific investigator,  the  second  that  of  the  inventor. 

In  view  of  the  scientific  discoveries  of  the  past  ten 
years,  which,  after  bringing  about  results  that  would 
have  seemed  chimerical  if  predicted,  leading  on  to 
the  extraction  of  a  substance  which  seems  to  set  the 
laws  and  limits  of  nature  at  defiance  by  radiating  a 
flood  of  heat,  even  when  cooled  to  the  lowest  point 
that  science  can  reach — a  substance,  a  few  specks  of 
which  contain  power  enough  to  start  a  railway  train, 
and  embody  perpetual  motion  itself,  almost  —  he 
would  be  a  bold  prophet  who  would  set  any  limit  to 
possible  discoveries  in  the  realm  of  nature.  We  are 
binding  the  universe  together  by  agencies  which  pass 
from  sun  to  planet  and  from  star  to  star.  We  are 
determined  to  find  out  all  we  can  about  the  myster- 
ious ethereal  medium  supposed  to  fill  all  space,  and 
which  conveys  light  and  heat  from  one  heavenly 
body  to  another,  but  which  yet  evades  all  direct  in- 
vestigation. We  are  peering  into  the  law  of  gravita- 
tion itself  with  the  full  hope  of  discovering  some- 
thing in  its  origin  which  may  enable  us  to  evade  its 
action.  From  time  to  time  philosophers  fancy  the 
road  open  to  success,  yet  nothing  that  can  be  prac- 
tically called  success  has  yet  been  reached  or  even 
approached.  When  it  is  reached,  when  we  are  able 
to  state  exactly  why  matter  gravitates,  then  will 
arise  the  question  how  this  hitherto  unchangeable 

334 


THE    FLYING-MACHINE 

force  may  be  controlled  and  regulated.  With  this 
question  answered  the  problem  of  the  interaction 
between  ether  and  matter  may  be  solved.  That 
interaction  goes  on  between  ethers  and  molecules  is 
shown  by  the  radiation  of  heat  by  all  bodies.  When 
the  molecules  are  combined  into  a  mass,  this  inter- 
action ceases,  so  that  the  lightest  objects  fly  through 
the  ether  without  resistance.  Why  is  this?  Why 
does  ether  act  on  the  molecule  and  not  the  mass? 
When  we  can  produce  the  latter,  and  when  the  mutual 
action  can  be  controlled,  then  may  gravitation  be 
overcome  and  then  may  men  build,  not  merely  air- 
ships, but  ships  which  shall  fly  above  the  air,  and 
transport  their  passengers  from  continent  to  con- 
tinent with  the  speed  of  the  celestial  motions. 

The  first  question  suggested  to  the  reader  by  these 
considerations  is  whether  any  such  result  is  possible ; 
whether  it  is  within  the  power  of  man  to  discover  the 
nature  of  luminiferous  ether  and  the  cause  of  gravita- 
tion. To  this  the  profoundest  philosopher  can  only 
answer,  "  I  do  not  know."  Quite  possibly  the  gates 
at  which  he  is  beating  are,  in  the  very  nature  of 
things,  incapable  of  being  opened.  It  may  be  that 
the  mind  of  man  is  incapable  of  grasping  the  secrets 
within  them.  The  question  has  even  occurred  to 
me  whether,  if  a  being  of  such  supernatural  power  as 
to  understand  the  operations  going  on  in  a  molecule 
of  matter  or  in  a  current  of  electricity  as  we  under- 
stand the  operations  of  a  steam-engine  should  essay 
to  explain  them  to  us,  he  would  meet  with  any  more 
success  than  we  should  in  explaining  to  a  fish  the 
engines  of  a  ship  which  so  rudely  invades  its  domain. 
As  was  remarked  by  William  K.  Clifford,  perhaps  the 
clearest  spirit  that  has  ever  studied  such  problems, 

335 


SIDE-LIGHTS    ON    ASTRONOMY 

it  is  possible  that  the  laws  of  geometry  for  spaces 
infinitely  small  may  be  so  different  from  those  of 
larger  spaces  that  we  must  necessarily  be  unable  to 
conceive  them. 

Still,  considering  mere  possibilities,  it  is  not  im- 
possible that  the  twentieth  century  may  be  destined 
to  make  known  natural  forces  which  will  enable  us 
to  fly  from  continent  to  continent  with  a  speed  far 
exceeding  that  of  the  bird. 

But  when  we  inquire  whether  aerial  flight  is  pos- 
sible in  the  present  state  of  our  knowledge ;  whether, 
with  such  materials  as  we  possess,  a  combination  of 
steel,  cloth,  and  wire  can  be  made  which,  moved  by 
the  power  of  electricity  or  steam,  shall  form  a  suc- 
cessful flying-machine,  the  outlook  may  be  altogether 
different.  To  judge  it  sanely,  let  us  bear  in  mind  the 
difficulties  which  are  encountered  in  any  flying-ma- 
chine. The  basic  principle  on  which  any  such  ma- 
chine must  be  constructed  is  that  of  the  aeroplane. 
This,  by  itself,  would  be  the  simplest  of  all  flyers, 
and  therefore  the  best  if  it  could  be  put  into  opera- 
tion. The  principle  involved  may  be  readily  com- 
prehended by  the  accompanying  figure.  A  M  is  the 
section  of  a  flat  plane  surface,  say  a  thin  sheet  of 
metal  or  a  cloth  supported  by  wires.  It  moves 
through  the  air,  the  latter  being  represented  by  the 
horizontal  rows  of  dots.  The  direction  of  the  mo- 
tion is  that  of  the  horizontal  line  A  P.  The  aero- 
plane has  a  slight  inclination  measured  by  the  pro- 
portion between  the  perpendicular  M  P  and  the 
length  A  P.  We  may  raise  the  edge  M  up  or  lower 
it  at  pleasure.  Now  the  interesting  point,  and  that 
on  which  the  hopes  of  inventors  are  based,  is  that 
if  we  give  the  plane  any  given  inclination,  even  one 

336 


THE    FLYING-MACHINE 

so  small  that  the  perpendicular  M  P  is  only  two  or 
three  per  cent,  of  the  length  A  M,  we  can  also  calculate 
a  certain  speed  of  motion  through  the  air  which,  if 


given  to  the  plane,  will  enable  it  to  bear  any  required 
weight.  A  plane  ten  feet  square,  for  example,  would 
not  need  any  great  inclination,  nor  would  it  require 
a  speed  higher  than  a  few  hundred  feet  a  second  to 
bear  a  man.  What  is  of  yet  more  importance,  the 
higher  the  speed  the  less  the  inclination  required,  and, 
if  we  leave  out  of  consideration  the  friction  of  the 
air  and  the  resistance  arising  from  any  object  which 
the  machine  may  carry,  the  less  the  horse-power  ex- 
pended in  driving  the  plane. 

Maxim  exemplified  this  by  experiment  several 
years  ago.  He  found  that,  with  a  small  inclination, 
he  could  readily  give  his  aeroplane,  when  it  slid  for- 
ward upon  ways,  such  a  speed  that  it  would  rise 
from  the  ways  of  itself.  The  whole  problem  of  the 
successful  flying  -  machine  is,  therefore,  that  of  ar- 
ranging an  aeroplane  that  shall  move  through  the 
air  with  the  requisite  speed. 

The  practical  difficulties  in  the  way  of  realizing 
the  movement  of  such  an  object  are  obvious.  The 
aeroplane  must  have  its  propellers.  These  must  be 
driven  by  an  engine  with  a  source  of  power.  Weight 
is  an  essential  quality  of  every  engine.  The  pro- 
pellers must  be  made  of  metal,  which  has  its  weak- 
ness, and  which  is  liable  to  give  way  when  its  speed 
attains  a  certain  limit.  And,  granting  complete  suc- 

337 


SIDE-LIGHTS    ON    ASTRONOMY 

cess,  imagine  the  proud  possessor  of  the  aeroplane 
darting  through  the  air  at  a  speed  of  several  hundred 
feet  per  second!  It  is  the  speed  alone  that  sustains 
him.  How  is  he  ever  going  to  stop  ?  Once  he  slack- 
ens his  speed,  down  he  begins  to  fall.  He  may,  in- 
deed, increase  the  inclination  of  his  aeroplane.  Then 
he  increases  the  resistance  to  the  sustaining  force. 
Once  he  stops  he  falls  a  dead  mass.  How  shall  he 
reach  the  ground  without  destroying  his  delicate 
machinery?  I  do  not  think  the  most  imaginative 
inventor  has  yet  even  put  upon  paper  a  demonstra- 
tively successful  way  of  meeting  this  difficulty.  The 
only  ray  of  hope  is  afforded  by  the  bird.  The  latter 
does  succeed  in  stopping  and  reaching  the  ground 
safely  after  its  flight.  But  we  have  already  men- 
tioned the  great  advantages  which  the  bird  possesses 
in  the  power  of  applying  force  to  its  wings,  which, 
in  its  case,  form  the  aeroplanes.  But  we  have  al- 
ready seen  that  there  is  no  mechanical  combination, 
and  no  way  of  applying  force,  which  will  give  to  the 
aeroplanes  the  flexibility  and  rapidity  of  movement 
belonging  to  the  wings  of  a  bird.  With  all  the  im- 
provements that  the  genius  of  man  has  made  in  the 
steamship,  the  greatest  and  best  ever  constructed  is 
liable  now  and  then  to  meet  with  accident.  When 
this  happens  she  simply  floats  on  the  water  until  the 
damage  is  repaired,  or  help  reaches  her.  Unless  we 
are  to  suppose  for  the  flying-machine,  in  addition  to 
everything  else,  an  immunity  from  accident  which  no 
human  experience  leads  us  to  believe  possible,  it 
would  be  liable  to  derangements  of  machinery,  any 
one  of  which  would  be  necessarily  fatal.  If  an  en- 
gine were  necessary  not  only  to  propel  a  ship,  but 
also  to  make  her  float — if,  on  the  occasion  of  any 

338 


THE    FLYING-MACHINE 

accident  she  immediately  went  to  the  bottom  with 
all  on  board — there  would  not,  at  the  present  day, 
be  any  such  thing  as  steam  navigation.  That  this 
difficulty  is  insurmountable  would  seem  to  be  a  very 
fair  deduction,  not  only  from  the  failure  of  all  at- 
tempts to  surmount  it,  but  from  the  fact  that  Maxim 
has  never,  so  far  as  we  are  aware,  followed  up  his 
seemingly  successful  experiment. 

There  is,  indeed,  a  way  of  attacking  it  which  may, 
at  first  sight,  seem  plausible.  In  order  that  the  aero- 
plane may  have  its  full  sustaining  power,  there  is  no 
need  that  its  motion  be  continuously  forward.  A 
nearly  horizontal  surface,  swinging  around  in  a  circle, 
on  a  vertical  axis,  like  the  wings  of  a  windmill  mov- 
ing horizontally,  will  fulfil  all  the  conditions.  In 
fact,  we  have  a  machine  on  this  simple  principle  in 
the  familiar  toy  which,  set  rapidly  whirling,  rises  in 
the  air.  Why  more  attempts  have  not  been  made  to 
apply  this  system,  with  two  sets  of  sails  whirling  in 
opposite  directions,  I  do  not  know.  Were  there  any 
possibility  of  making  a  flying-machine,  it  would  seem 
that  we  should  look  in  this  direction. 

The  difficulties  which  I  have  pointed  out  are  only 
preliminary  ones,  patent  on  the  surface.  A  more 
fundamental  one  still,  which  the  writer  feels  may 
prove  insurmountable,  is  based  on  a  law  of  nature 
which  we  are  bound  to  accept.  It  is  that  when  we 
increase  the  size  of  any  flying-machine  without 
changing  its  model  we  increase  the  weight  in  propor- 
tion to  the  cube  of  the  linear  dimensions,  while  the 
effective  supporting  power  of  the  air  increases  only 
as  the  square  of  those  dimensions.  To  illustrate  the 
principle  let  us  make  two  flying-machines  exactly 
alike,  only  make  one  on  double  the  scale  of  the  other 

339 


SIDE-LIGHTS    ON    ASTRONOMY 

in  all  its  dimensions.  We  all  know  that  the  volume 
and  therefore  the  weight  of  two  similar  bodies  are 
proportional  to  the  cubes  of  their  dimensions.  The 
cube  of  two  is  eight.  Hence  the  large  machine  will 
have  eight  times  the  weight  of  the  other.  But  sur- 
faces are  as  the  squares  of  the  dimensions.  The 
square  of  two  is  four.  The  heavier  machine  will 
therefore  expose  only  four  times  the  wing  surface  to 
the  air,  and  so  will  have  a  distinct  disadvantage  in 
the  ratio  of  efficiency  to  weight. 

Mechanical  principles  show  that  the  steam  press- 
ures which  the  engines  would  bear  would  be  the 
same,  and  that  the  larger  engine,  though  it  would 
have  more  than  four  times  the  horse-power  of  the 
other,  would  have  less  than  eight  times.  The  larger 
of  the  two  machines  would  therefore  be  at  a  disad- 
vantage, which  could  be  overcome  only  by  reducing 
the  thickness  of  its  parts,  especially  of  its  wings,  to 
that  of  the  other  machine.  Then  we  should  lose  in 
strength.  It  follows  that  the  smaller  the  machine 
the  greater  its  advantage,  and  the  smallest  possible 
flying-machine  will  be  the  first  one  to  be  successful. 

We  see  the  principle  of-  the  cube  exemplified  in  the 
animal  kingdom.  The  agile  flea,  the  nimble  ant,  the 
swift-footed  greyhound,  and  the  unwieldy  elephant 
form  a  series  of  which  the  next  term  would  be  an 
animal  tottering  under  its  own  weight,  if  able  to  stand 
or  move  at  all.  The  kingdom  of  flying  animals  shows 
a  similar  gradation.  The  most  numerous  fliers  are  lit- 
tle insects,  and  the  rising  series  stops  with  the  condor, 
which,  though  having  much  less  weight  than  a  man, 
is  said  to  fly  with  difficulty  when  gorged  with  food. 

Now,  suppose  that  an  inventor  succeeds,  as  well  he 
may,  in  making  a  machine  which  would  go  into  a 


THE    FLYING-MACHINE 

watch-case,  yet  complete  in  all  its  parts,  able  to  fly 
around  the  room.  It  may  carry  a  button,  but  noth- 
ing heavier.  Elated  by  his  success,  he  makes  one 
on  the  same  model  twice  as  large  in  every  dimension. 
The  parts  of  the  first,  which  are  one  inch  in  length, 
he  increases  to  two  inches.  Every  part  is  twice  as 
long,  twice  as  broad,  and  twice  as  thick.  The  result 
is  that  his  machine  is  eight  times  as  heavy  as  before. 
But  the  sustaining  surface  is  only  four  times  as  great. 
As  compared  with  the  smaller  machine,  its  ratio  of 
effectiveness  is  reduced  to  one-half.  It  may  carry 
two  or  three  buttons,  but  will  not  carry  over  four, 
because  the  total  weight,  machine  plus  buttons,  can 
only  be  quadrupled,  and  if  he  more  than  quadruples 
the  weight  of  the  machine,  he  must  less  than  quad- 
ruple that  of  the  load.  How  many  such  enlargements 
must  he  make  before  his  machine  will  cease  to  sustain 
itself,  before  it  will  fall  as  an  inert  mass  when  we  seek 
to  make  it  fly  through  the  air?  Is  there  any  size  at 
which  it  will  be  able  to  support  a  human  being  ?  We 
may  well  hesitate  before  we  answer  this  question  in 
the  affirmative. 

Dr.  Graham  Bell,  with  a  cheery  optimism  very 
pleasant  to  contemplate,  has  pointed  out  that  the 
law  I  have  just  cited  may  be  evaded  by  not  making 
a  larger  machine  on  the  same  model,  but  changing  the 
latter  in  a  way  tantamount  to  increasing  the  num- 
ber of  small  machines.  This  is  quite  true,  and  I  wish 
it  understood  that,  in  laying  down  the  law  I  have 
cited,  I  limit  it  to  two  machines  of  different  sizes  on 
the  same  model  throughout.  Quite  likely  the  most 
effective  flying-machine  would  be  one  carried  by  a 
vast  number  of  little  birds.  The  veracious  chron- 
icler who  escaped  from  a  cloud  of  mosquitoes  by 


SIDE-LIGHTS    ON    ASTRONOMY 

crawling  into  an  immense  metal  pot  and  then  amused 
himself  by  clinching  the  antennre  of  the  insects  which 
bored  through  the  pot  until,  to  his  horror,  they  be- 
came so  numerous  as  to  fly  off  with  the  covering, 
was  more  scientific  than  he  supposed.  Yes,  a  suffi- 
cient number  of  humming-birds,  if  we  could  combine 
their  forces,  would  carry  an  aerial  excursion  party 
of  human  beings  through  the  air.  If  the  watch-maker 
can  make  a  machine  which  will  fly  through  the  room 
with  a  button,  then,  by  combining  ten  thousand  such 
machinesfhe  may  be  able  to  carry  a  man.  But  how 
shall  the  combined  forces  be  applied? 

The  difficulties  I  have  pointed  out  apply  only  to 
the  fly  ing -machine  properly  so-called,  and  not  to 
the  dirigible  balloon  or  airship.  It  is  of  interest  to 
notice  that  the  law  is  reversed  in  the  case  of  a  body 
which  is  not  supported  by  the  resistance  of  a  fluid  in 
which  it  is  immersed,  but  floats  in  it,  the  ship  or 
balloon,  for  example.  When  we  double  the  linear 
dimensions  of  a  steamship  in  all  its  parts,  we  in- 
crease not  only  her  weight  but  her  floating  power, 
her  carrying  capacity,  and  her  engine  capacity  eight- 
fold. But  the  resistance  which  she  meets  with  when 
passing  through  the  water  at  a  given  speed  is  only 
multiplied  four  times.  Hence,  the  larger  we  build 
the  steamship  the  more  economical  the  application 
of  the  power  necessary  to  drive  it  at  a  given  speed. 
It  is  this  law  which  has  brought  the  great  increase 
in  the  size  of  ocean  steamers  in  recent  times.  The 
proportionately  diminishing  resistance  which,  in  the 
flying-machine,  represents  the  floating  power  is,  in 
the  ship,  something  to  be  overcome.  Thus  there 
is  a  complete  reversal  of  the  law  in  its  practical  ap- 
plication to  the  two  cases. 

342 


THE    FLYING-MACHINE 

The  balloon  is  in  the  same  class  with  the  ship. 
Practical  difficulties  aside,  the  larger  it  is  built  the 
more  effective  it  will  be,  and  the  more  advantageous 
will  be  the  ratio  of  the  power  which  is  necessary  to 
drive  it  to  the  resistance  to  be  overcome. 

If,  therefore,  we  are  ever  to  have  aerial  navigation 
with  our  present  knowledge  of  natural  capabilities, 
it  is  to  the  airship  floating  in  the  air,  rather  than  the 
flying-machine  resting  on  the  air,  to  which  we  are  to 
look.  In  the  light  of  the  law  which  I  have  laid  down, 
the  subject,  while  not  at  all  promising,  seems  worthy 
of  more  attention  than  it  has  received.  It  is  not  at 
all  unlikely  that  if  a  skilful  and  experienced  naval 
constructor,  aided  by  an  able  corps  of  assistants, 
should  design  an  airship  of  a  diameter  of  not  less 
than  two  hundred  feet,  and  a  length  at  least  four  or 
five  times  as  great,  constructed,  possibly,  of  a  textile 
substance  impervious  to  gas  and  borne  by  a  light 
framework,  but,  more  likely,  of  exceedingly  thin 
plates  of  steel  carried  by  a  frame  fitted  to  secure  the 
greatest  combination  of  strength  and  lightness,  he 
might  find  the  result  to  be,  ideally  at  least,  a  ship 
which  would  be  driven  through  the  air  by  a  steam- 
engine  with  a  velocity  far  exceeding  that  of  the  fleet- 
est Atlantic  liner.  Then  would  come  the  practical 
problem  of  realizing  the  ship  by  overcoming  the 
mechanical  difficulties  involved  in  the  construction 
of  such  a  huge  and  light  framework.  I  would  not  be 
at  all  surprised  if  the  result  of  the  exact  calculation 
necessary  to  determine  the  question  should  lead  to 
an  affirmative  conclusion,  but  I  am  quite  unable  to 
judge  whether  steel  could  be  rolled  into  parts  of  the 
size  and  form  required  in  the  mechanism. 

In  judging  of  the  possibility  of  commercial  success 
33  343 


SIDE-LIGHTS    ON    ASTRONOMY 

the  cheapness  of  modern  transportation  is  an  element 
in  the  case  that  should  not  be  overlooked.  I  believe 
the  principal  part  of  the  resistance  which  a  limited 
express  train  meets  is  the  resistance  of  the  air.  This 
would  be  as  great  for  an  airship  as  for  a  train.  An 
important  fraction  of  the  cost  of  transporting  goods 
from  Chicago  to  London  is  that  of  getting  them  into 
vehicles,  whether  cars  or  ships,  and  getting  them  out 
again.  The  cost  of  sending  a  pair  of  shoes  from  a 
shop  in  New  York  to  the  residence  of  the  wearer  is, 
if  I  mistake  not,  much  greater  than  the  mere  cost  of 
transporting  them  across  the  Atlantic.  Even  if  a 
dirigible  balloon  should  cross  the  Atlantic,  it  does 
not  follow  that  it  could  compete  with  the  steamship 
in  carrying  passengers  and  freight. 

I  may,  in  conclusion,  caution  the  reader  on  one 
point.  I  should  be  very  sorry  if  my  suggestion  of 
the  advantage  of  the  huge  airship  leads  to  the  sub- 
ject being  taken  up  by  any  other  than  skilful  en- 
gineers or  constructors,  able  to  grapple  with  all 
problems  relating  to  the  strength  and  resistance  of 
materials.  As  a  single  example  of  what  is  to  be 
avoided  I  may  mention  the  project,  which  sometimes 
has  been  mooted,  of  making  a  balloon  by  pumping 
the  air  from  a  very  thin,  hollow  receptacle.  Such  a 
project  is  as  futile  as  can  well  be  imagined;  no 
known  substance  would  begin  to  resist  the  necessary 
pressure.  Our  aerial  ship  must  be  filled  with  some 
substance  lighter  than  air.  Whether  heated  air  would 
answer  the  purpose,  or  whether  we  should  have  to  use 
a  gas,  is  a  question  for  the  designer. 

To  return  to  our  main  theme,  all  should  admit  that 
if  any  hope  for  the  flying  -  machine  can  be  enter- 
tained, it  must  be  based  more  on  general  faith  in 

344  • 


THE    FLYING-MACHINE 

what  mankind  is  going  to  do  than  upon  either  rea- 
soning or  experience.  We  have  solved  the  problem 
of  talking  between  two  widely  separated  cities,  and 
of  telegraphing  from  continent  to  continent  and 
island  to  island  under  all  the  oceans — therefore  we 
shall  solve  the  problem  of  flying.  But,  as  I  have 
already  intimated,  there  is  another  great  fact  of 
progress  which  should  limit  this  hope.  As  an  al- 
most universal  rule  we  have  never  solved  a  problem 
at  which  our  predecessors  have  worked  in  vain,  un- 
less through  the  discovery  of  some  agency  of  which 
they  have  had  no  conception.  The  demonstration 
that  no  possible  combination  of  known  substances, 
known  forms  of  machinery,  and  known  forms  of 
force  can  be  united  in  a  practicable  machine  by  which 
men  shall  fly  long  distances  through  the  air,  seems  to 
the  writer  as  complete  as  it  is  possible  for  the  demon- 
stration of  any  physical  fact  to  be.  But  let  us  dis- 
cover a  substance  a  hundred  times  as  strong  as  steel, 
and  with  that  some  form  of  force  hitherto  unsuspect- 
ed which  will  enable  us  to  utilize  this  strength,  or  let 
us  discover  some  way  of  reversing  the  law  of  gravita- 
tion so  that  matter  may  be  repelled  by  the  earth  in- 
stead of  attracted — then  we  may  have  a  flying-ma- 
chine. But  we  have  every  reason  to  believe  that 
mere  ingenious  contrivances  with  our  present  means 
and  forms  of  force  will  be  as  vain  in  the  future  as 
they  have  been  in  the  past. 


INDEX 


ABBOTT,  C.  G.,  work  of,  108. 
Aeroplane,  principle  of,  336. 
Airship  made  practicable,  342. 
Airy,     Professor,     reports      no 

Observatory    in    the    United 

States,  282. 
American   astronomers,    honors 

received  by,  119. 
American      Nautical     Almanac 

founded,  199. 
Astronomy,    world's    debt    to, 

216;     applied    to    determine 

positions  on  the  earth,  217; 

American,  aspects  of,  274. 
Attraction     of     the     heavenly 

bodies,  how  measured,  134. 
Axis  of  earth,  wobbling  of,  219. 

BALLOON,  dirgible,  advantage 
of,  342. 

Bell,  Professor  Graham,  law  of 
the  cube,  341. 

Bessel,  stellar  parallax,  66. 

Bigelow,  Professor,  sun-spots 
and  magnetic  storms,  307. 

Bond,  Professor,  makes  astro- 
nomical observations,  283. 

Bowditch,  his  translation  of 
Laplace,  282. 

Buraham,  S.  W.,  observes  double 
stars,  94. 

CAMPBELL,  PROFESSOR,  meas- 
ures motions  of  the  stars,  117; 
observations  on  Mars,  129; 
motion  of  1830  Groombridge, 

3°S- 
Canopus,   parallax  of,  43;  im- 


measurable distance  of,  306. 


Carnegie  Institution,  work  of, 

107. 
Chart,     photographic,     of     the 

stars,  112. 
Chase,   Dr.,   parallaxes  of  the 

stars,  115. 

Chicago,  beginnings  of,  283. 
Chicago    University,    work    of, 

294. 

Clarke,  Alvan,  maker  of  tele- 
scopes, 78. 

Clouos,  how  formed,  184. 
Columbus,  observations  on  the 

compass,  151. 

Comets,  how  searched  for,  270. 
Comet-seeker,  how  made,  101. 
Compass,    the    mariner's,    140; 

history  of,  152;  effect  of  iron 

upon,  153. 

Copernicus,  his  philosophy,  32. 
Corona  of  the  sun,  14. 
Creation,  unity  of,  19. 
Crossley  reflector  at    the    Lick 

Observatory,  113. 
Curie,  discovery  of  radium,  29. 

DAVIS,  REAR-ADMIRALCHARLES 
HENRY,  199;  superintends 
preparation  of  Nautical  Al- 
manac, 199;  his  translation 
of  Ganss,  291. 

Delaunay,  work  of,  210. 

Distances  of  the  stars,  i. 

Dollond  invents  achromatic  tele- 
scope, 77. 

Draper  Memorial,  work  of,  at 
Harvard,  115. 


EARTH,  rotation  of,  16. 


347 


SIDE-LIGHTS    ON    ASTRONOMY 


Eclipse,  total  solar,  error  of  pre- 
diction, 1 1 8. 

Eclipses,  total,  14. 

Ephemerides,  astronomical,  193. 

Ephemeris,  astronomical,  191. 

Eugenics,  a  new  science,  175. 

Extent  of  universe,  how  esti- 
mated, 68. 

FAIRYLAND  of  geometry,  155. 
Flying-machine,     outlook     for, 

330;    difficulties  in  designing, 

331;     conditions    of.  success, 

334- 
Force,  dispute  as  to  meaning  of, 

320. 
Fraunhofer,  maker  of  telescopes, 

78. 
Frost,  Professor  E.  B.,  work  at 

Yerkes  Observatory,  117. 

G-ALTON,  FRANCIS,  promotes  eu- 

genics   175. 

Lregenschem,  appearance  of,  15. 
Geometry,  fairyland  of,  155. 
Gilliss,      Captain      James     M., 

founds    Naval    Observatory, 

284. 

Gill,  parallaxes  of  stars,  43. 
Gill,    photographs    of    southern 

stars,  in. 
Glass,  optical,  how  made  with 

purity,  79. 

Gravitation,  control  of,  335. 
Great  Bear,  constellation  of,  the 

"  Cynosure,"  191. 
Greenwich,  origin  of  longitudes, 


HANSEN  investigates  motion  of 
the  moon,  210. 

Hale,  Professor  George  E.,  sys- 
tem of  photographing  the  sun, 
107. 

Heat,  of  sun,  origin  of,  8;  how 
kept  up,  28;  of  the  stars, 
source  of,  56. 

Hell,  Father,  his  work,  227. 

Herschel,  form  of  the  universe,  40 . 

Huggins,  Sir  William,  life  his- 
tory of  the  stars,  115. 

Huxley,  the  army  of  science,  1 89. 


INHABITABILITY  of  other  worlds, 

122. 

Investigator,  the  scientific,  evo- 
lution of,  236. 

JUPITER,  physical  constitution 
of,  13;  appearance  of,  99; 
satellites  of,  99 ;  red  spots  on, 
105;  a  miniature  sun,  118; 
rotation  of,  118;  satellites, 
prediction  of  phenomena,  204. 

KANT,  views  of  the  universe,  31. 

Kapteyn,  Professor  J.  C.,  cata- 
logues the  stars,  1 1 1 ;  paper 
on  color  of  Milky  Way  stars, 
302. 

Keeler,  photographs  of  nebulae, 

113- 
Kelvin,  Lord,  possible  number 

of  stars,  5 1 ;  possible  origin  of 

life,  123. 
Kiistner,  variations  of  latitude, 

292. 

LAGRANGE  transplanted  to  Par- 
is, 171. 

Langley,  Professor,  work  of, 
1 08;  his  flying-machine,  330. 

Language,  imperfections  of,  324 ; 
mathematical,  advantage  of, 
328. 

Latitudes,  variation  of,  118,  272. 

Lenses,  how  ground,  81. 

Le  Verrier,  work  of,  210. 

Lick  _  Observatory,  importance 
of  its  work,  289. 

Life  in  the  universe,  120;  con- 
ditions of,  121 ;  origin  of,  123. 

Light,  motion  through  space,  9; 
possible  extinction  of,  in 
space,  53. 

Littrow,  accuses  Hell  of  forgery, 

233- 

Longitudes,  telegraphic  determi- 
nation of,  285. 

Loomis,  Professor  Elias,  founds 
observatory,  284. 

Lowell,  Percival,  observes  canals 
of  Mars,  98,  271. 

Lyrae,  constellation,  our  journey 
towards,  i,  163. 


348 


INDEX 


MAGNET,  properties  of,  142;  dip 
of,  146-148. 

Magnetic,  force,  141;  needle, 
variation  of,  145;  storms,  re- 
lation to  sun-spots,  307. 

Magnetism  of  the  earth,  141. 

Mars,  surface  of,  12,  98;  canals 
of,  98;  possible  inhabitants 
of,  127;  observed  by  Camp- 
bell, 129;  possible  atmosphere 
of,  129,  271. 

Mathematical  language,  advan- 
tages of,  328. 

Matter,  possible  evolution  of,  58. 

Maxim,  experiment  with  aero- 
plane, 337. 

Mercury,  motion  of  orbit,  16; 
visibility  of,  100. 

Meridians,  confusion  of,  191; 
prime  use  of,  191. 

Meteoric  matter,  possibilities  of, 

Milky    Way,    structure    of,    6; 

probable  distance  of,  25;    as 

a  spectacle,  61. 
Mitchell,   Professor   O.   M.,   his 

lectures,  287. 
Moon,  absence  of  life  on,  10,  127; 

enigma  of  its  motion,  117. 

NAUTICAL  ALMANAC,  191. 
Nebulae,  photographs  of,  113. 
Neptune,  visibility  of,  100. 
New  stars,  blazing  out  of,  22. 

OPTICAL  glass,  how  made  with 

purity,  79. 
Orion,  nebulae  of,  104. 

PARALLAX     of    stars,     difficult 

problem  of,  43. 
Paris    Academy    of     Sciences, 

early  work  of,  167. 
Pearson,     Karl,     mathematical 

investigations,  176. 
Pierce,  Professor,  tables  of  the 

moon,  213;    perturbations  of 

Uranus,  286. 

P6l6e,  Mount,  effects  of  its  erup- 
tion, 109. 
Perseus,  new  star  of  1902,  23; 

probable  distance  of,  24. 


Photography,  use  in  astronomy, 
106. 

Pickering,  Professor,  photo- 
graphs of  the  stars,  112. 

Planets,  outer,  constitution  of, 
131;  how  weighed,  133. 

Potsdam,  Germany,  observa- 
tions at,  1 06. 

Ptolemy,  fixes  length  of  year, 
220. 

Publications,  scientific,  number 
of,  173- 

RADIUM,   enigma    of    its    heat, 

3°- 

Rain,  possibilities  of  producing, 
182. 

Rays  and  corpuscles,  20;  possi- 
ble speed  of,  27. 

Research,  proper  motions  of, 
4;  scientific,  organization  of, 
16*. 

Rigel,  parallax  of,  43 ;  immeas- 
urable distance  of,  306. 

Rittenhouse,  first  American  as- 
tronomer, 282. 

Royal  Society,  early  work  of, 
167. 

SATURN,  when  best  seen,  95; 
spots  on,  96;  rotation  of,  97. 

SchiaparelU,  observations  of 
Mars,  271. 

Science,  specialization  of,  19; 
true  spirit  of,  313. 

Sciences,  classification  of,  172. 

Scientific  method,  relation  of,  to 
social  progress,  312. 

Smithsonian  Institution,  its 
Astro  -  Physical  Observatory, 
108. 

Stars,  distance  of,  i;  new,  22; 
nearest,  distance  of,  45 ;  prop- 
er motions,  speed  of,  46,  48; 
arrangements  in  space,  49; 
total  light  of,  52;  now  scat- 
tered in  space,  70 ;  cluster  in 
Perseus,  103;  catalogue  of, 
no;  variable,  116;  measures 
of  motions  to,  and  their  use, 
116. 

Sun-dial,  formerly  used,  220. 


349 


SIDE-LIGHTS    ON    ASTRONOMY 


Sun,  possible  age  of,  57;    spots 

of,  how  seen,  101. 
Sun's  heat,  possible  change  in, 

109. 
Sun-spots,  eleven-year  cycle  of, 

21. 

TABLES,  astronomical,  use  of, 
205. 

Telescope,  making  of,  76;  great, 
of  Yerkes  Observatory,  79; 
how  tested,  86;  primitive, 
mounting  of,  88-90;  reflect- 
ing. 93- 

Thome,  Dr.,  his  work  at  Cordova, 
in. 

Time,  distribution  of,  221. 

UNITY  of  creation,  19. 

Universe,  extent  of,  5;  ancient 
and  modern  views  of,  33 ;  pos- 
sible limits,  42;  possible  age 
of,  55;  duration  of,  59;  ex- 
tent of,  60;  symmetry  of,  64; 


extent  of,  how  estimated,  65; 
as  an  organism,  300. 

VENUS,  rotation  of,  10;  transit 
of,  ii ;  atmosphere  of,  n; 
clouds  in  its  atmosphere,  129; 
transit  of,  in  1769,  230;  tran- 
sit of,  in  1769,  observations  of, 
281. 

WALKER,  SEARS  COOK,  investi- 
gates motion  of  Neptune,  285. 

Wallace,  Alfred  Russel,  views 
of,  criticised,  125. 

Will,  freedom  of,  321. 

Winthrop,  Professor,  makes 
astronomical  observations, 
281. 

YERKES  OBSERVATORY,  motions 
of  the  stars,  117. 

ZODIACAL  light,  appearance  of, 


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